Certainly one way to define the Personal Computer stems from the era of the IBM PC: a gray box with a monitor, mouse, and keyboard (or a laptop). But the idea of the Personal Computer dates back quite a while — back to Alan Kay's Dynabook, the Lisp Machine, etc.
The Apple Knowledge Navigator provided a vision of personal computing far more dynamic than that dull gray box. Although still a pale comparison, tablet and phone platforms are beginning to look awfully similar.
The essence of those pre-PC Personal Computers was that of the user controlling the device. You control the data, you control the software; the Personal Computer is a uniquely personal artifact that the user adapts to his own working style. One consequence of this is that creating is as easy (perhaps easier) as consuming content. Another nice side effect is that your data remains private by virtue of local storage.
In many ways, then, a tablet or phone comes significantly closer to a personal computer than that dull gray box under your desk. For example, on Android, the screen ceases to be a place to throw icons and becomes a rich canvas of widgets. Additionally, my phone fits into my pocket and is always there. Ubiquitous cellular coverage gives me access to my data from most anywhere. The touchscreen and interface conventions make direct manipulation shine in a way you just can't get from a screen two feet away on a desk.
And, those are just superficial improvements over the desktop. Albeit tied to proprietary services, Google's voice search and Siri are inching closer to the dream of personal Intelligent Agents reminding us all that our mothers called us earlier today and want us to pick up the birthday cake for the surprise party With a few taps I can search basically all of my data, not to mention the collective knowledge of mankind.
But the software running on these devices has a dark side. Want to access your music collection the go? You have to get it from Google Play. Want to have lightweight instant messaging? You have to use GTalk. Or take ebook readers (certainly personal devices): that book you just downloaded to your Kindle is DRMed and stuck there! That intelligent agent? Apple records everything you bark at her and can take her away at a moment's notice.
Furthermore, the software on these devices is geared almost exclusively toward content consumption. You can listen to music all day long, but don't try multi-track recording. That ebook reader is great for reading, but you can't scratch notes in the margins of any of your books or sit down with one and scrawl out your latest manuscript. Clearly, some of this is from the youth of these new systems, but it is distressing to see them geared first toward consumption (the Newton, for example, was geared from the start as a device for creation).
The "cloud" as implemented by Amazon, Google, Apple, et al. is a distinct threat to the personal computer. Loss of control over our own data is perhaps the worst part of the cloud. We're easily seduced by genuinely useful features like access to our contacts and music from any device without having to manually sync anything. It's certainly more convenient to purchase a digital movie on Amazon Prime than to hunt down a DVD, and Netflix is definitely nicer for most people than cable television. But when you buy a movie on Amazon, you don't really own it.
Underlying many of these cloud services (especially media-related ones) is Digital Restrictions Management. Whether it be the files themselves or the protocol used to transmit data, DRM is used to control what you can do with your data, restricting even what programs you can use to interact with seemingly neutral files. Worse, networked DRM services can and have led to lost data when it is no longer profitable for the company to run the verification servers.
The only copying that DRM discourages effectively is the sneakernet. And, given that the sneakernet has existed since recordable media has existed, it doesn't seem like the sneakernet is really much of a threat to creative business. I might lend a friend a CD (or even let her copy a few files), but just as I don't unwrap that CD and torrent it through The Pirate Bay, I'm not going to download a movie from Amazon and do the same. There's really no incentive to do so, for most people — most people pirate because that's what you have to do to get the media you want, not because you have a compulsive desire to share things with your closest 10,000 friends.
In order to prevent what is effectively sharing between actual friends, pushers of DRM-infected data want us to completely cede control of our own data!
And they have made people accept it: Steam, Netflix, and Amazon Prime are wildly popular. All of those services are great ideas, but all of them treat you as if you were a criminal.
Worse yet, the spread of Software-as-a-Service is returning us to the bad old days: that powerful PC in your pocket is quickly becoming no more than a glorified terminal. The open peer-to-peer network is being subverted from an enabler of collaboration never before seen into yet another scheme to tether users to proprietary, centralized services. And, as SaaS expands, privacy recedes. No longer is it implicit that your documents are yours alone; now you write and store things using Google Docs and have no expectation of privacy (legally), despite expecting privacy. Amazon knows what you read; Netflix knows what you watch; Google knows what you visit.
Control over the programs you run, and more importantly can write, is key to a personal computer being personal. And it seems absurd that that right might be taken away, but behold: the iPhone and soon Mac Store are these mythical walled gardens. You have to subvert your device to gain real control! And the natural path for Apple is to restrict Macs similarly to iOS devices.
And so we are all-too-near an Orwellian nightmare where vendors dictate what we can do with and how we can use our own data.
But what about the hardware itself? It could be argued that a device isn't really personal for some set of people if they can't change all of the software. Here too we see some promise, and some pitfalls.
The shift to tablet and phone hardware has meant a shift from x86 machines running PC BIOS to thousands of ARM boards, each with its own peculiar way of being programmed. Things you take for granted on x86, like being able to even boot, require custom code. And let's not even begin talking about all of the DSPs and co-processors. Vendors aren't always forthcoming with documentation for their boards, and, even worse, those that do port Linux to their hardware often blatantly violate the GPL and do not distribute kernel sources. This restricts the utility of perfectly fine hardware: often to the detriment of the user and to the benefit of the manufacturer.
Anyone who finds they can't upgrade to the latest version of Android because their vendor won't support it, and the community cannot support it because of non-free drivers, knows what losing control over their hardware is like (RIP HTC Dream).
It might seem like a minor setback ("I guess I have to buy a new phone"), but the lack of specifications or support marginalizes alternative operating systems. There's Meego, Tizen, Open webOS, Firefox OS, SHR, etc., but experimenting with them on your device is a non-starter. Imagine if the x86 were so closed (something we may not have to only imagine much longer): it is doubtful that GNU/Linux or the multitude "alternative" OSes would exist (Atheos, Haiku, L4Linux, even the Hurd). Ever more closed hardware is putting us into a position where two or three companies will dictate everything about the computing experience going forward, with no room for freethinking tinkerers to revolutionize how we interact with our devices.
We are staring at a bleak future, and living in a bleak present in some ways. But there is hope for the battle to be won by the Personal Computer instead of the Terminal.
The Internet is not yet merely glorified cable television. Hypertext, email, instant messaging, trivial file transfer, etc. have revolutionized how mankind communicates (understatement of the decade). Once upon a time the dream was that everyone would be a first-class netizen: your IP was publicly routeable and with a bit of know-how you had a server. Instead, thanks to grossly asymmetric pipes and heavy NATing, it is rare for any individual to run their own servers. Instead we turn to Google, Amazon, et al and cede control over our data.
But now broadband connections are spreading fast (I've gone from 100Kbit/s to 2Mbit/s upstream in three years just with basic service), IPv6 is really here, and software is being written to challenge the centralized "cloud" model being pushed on us from above.
We've had a few victories already: SMTP is still in use, XMPP is the dominant chat protocol (and IRC refuses to die), RSS/Atom aggregation decentralizes news, and the core network protocols are developed in the open.
But Google still controls Android, and myriad services control your data. Part of this is because they have easy client and server interfaces; sure you could run gallery2 and Wordpress on your own server, but I can just snap a photo on my phone and it's up on Facebook 40 seconds later (well, if their app worked, it would be).
Luckily, there are people working on making easy to use "cloud" services. In particular, ownCloud. ownCloud provides a framework for hosting and syncing data between your devices and sharing data with others. The important part is not so much the central server, but the clients they are writing. Eventually, it should be possible to e.g. replace the Google contact/mail/calendar sync and Google Drive, while adding these features to the desktop. Integration in KDE is already underway.
Imagine, instead of being tied to Google you could move the central server to the hosting provider of your wish (or pack up your data and move it to greener pastures if you're not running your own). And, perhaps more subtle (but the real liberation): Your data would be freely movable between all operating systems (interesting that you have to go through hoops to sync your GMail contacts with anything else, and Abandon All Hope Ye who wants to share between an Apple device and anything else). Additionally, the server is designed to respect your privacy (you can e.g. only store encrypted data server-side).
On the hardware side, projects like Firefox OS are very important: having a "mobile" Free Software OS developed in the open might be essential when the dominant open platforms are developed monolithically by corporations with no interest in protecting user control of data.
And then for developing the next generation of devices, folks like Rhombus Tech are pushing for the development of interchangeable CPU boards for embedded devices, and the FSF is expanding their focus to include open hardware.
There are two serious threats that would undermine any resistance: IPv4 exhaustion and draconian content policing. The former issue is technical and likely to solve itself: in the long run multi-level NAT would be too costly, switching hardware will be replaced as it is obsoleted, etc. The latter is political and represents the most serious threat of all. If we cannot communicate freely and the pipes are owned by the very organizations whose business interests will be harmed... we've already seen how brazen the current IP regime can be, and it will take vigilance on the part of many to prevent them from having their way.
Where will we be in ten years? If Google, Amazon, Apple, and Old Media get their way, in a new dark age of computing. Certainly, you'll have a fancy tablet and access to infinite entertainment. But you will own nothing. Sharing data will be controlled by a chosen few entities, the programs you can run or write will be limited in the name of security, and privacy will be dead.
History shows that personal computing survived despite Apple and Microsoft in the 80s and 90s. So, I'm hopeful that other forces will win: the forces of Free Culture and Free Software. If they succeed (or are at least not crushed), the future is much brighter: most content will be available DRM-free, users will control their computing environments, and the egalitarian promise of the Internet will be realized (in no small part thanks to IPv6).