Well, MSFT does actually have a fair amount of office space and employees in the Valley, so I'm not sure the effect would actually be that great. The "SVC" (Silicon Valley Campus) actually houses some interesting projects.. I think, from Googling, those include: Hotmail, MSNTV, parts of XBox, parts of PowerPoint, etc.

See the following for locations: http://www.microsoft.com/about/companyinformation/usaoffices...