Just a quickie: Joe Beda has a post about Google's 20% benefit.
There have been plenty of times I've gazed through the window trying to figure out how this kind of thing could work for Microsoft because I really, really want all these smart people at Microsoft to unleash disruptive innovation. Seeing Joe's context-setting of how it works for Google makes me realize that it would be really, really hard to get this to work at One Microsoft Way.
There are people who serve as jealous guardians to some parts of the source code for their team's product. Woe unto you should you go and randomly check something in, even if it's not breaking anything. They might as well fly into your room in a swirling fit of red robes - " Dost thou knowest what great sin thou hath wrought upon the repository!?! "
It's weird. And the longer you're in the group, the more you naturally accede to these self-appointed feature-priests until the offerings and deference just become business as usual. Whew, some groups really need some heavy people rotation, if only to free the source code from their oversight.