jones_supa writes: After leaving his position as CEO of Microsoft a year ago, Steve Ballmer has still held a position as a member of the board of directors for the company. Now, he is leaving the board, explaining why in a letter to fresh Microsoft CEO Satya Nadella. "I have become very busy," Ballmer explains. "I see a combination of Clippers, civic contribution, teaching and study taking up a lot of time." Despite his departure, the former-CEO is still invested in the company's success, and he spent most of the letter encouraging Nadella and giving advice. Nadella shot back a supportive, equally optimistic response, promising that Microsoft will thrive in "the mobile-first, cloud-first world."