Ex-Xbox chief Don Mattrick lands at Zynga, officially (update: Ballmer memo)

We just got the news that ex-head of Xbox, Don Mattrick, was out at Microsoft, and now we know where he's going: Zynga. AllThingsD reports that Mattrick is officially the new CEO of the casual social gaming firm, and Mark Pincus, the current CEO, is stepping down from that position to make room for Mattrick's arrival. Fear not for Pincus, however, as the founder of Zynga will maintain a role at the company as chairman and chief product officer. Naturally, Zynga's thrilled with the hire, though w...