Microsoft KIN manager moves to Yahoo2
The potentially disconcerting part of Matheny's departure from Microsoft is that he was in charge of the Windows Phone 7 App Studio, and was responsible for setting it apart. Perhaps he has already done all he could for Windows Phone 7, but it's odd that he's leaving before the release.
Looking at the best case scenario, Microsoft willingly let Matheny join Yahoo because he had given all he could to the Windows Phone 7 project. The worst case scenario, however, is that Matheny jumped ship from the Windows Phone 7 project, recognizing that it wouldn't prove a legitimate competitor to the current market leaders.