I worked very close to Chris in 2003 when I just become the Dev Manager of Search. Chris was just getting back to Microsoft after a few years at Amazon, and my manager, John Krass, reported to him.
Chris was (is) an outstanding Vice President at Microsoft. He was super smart, engaging and business oriented. He was not "dev smart", but he was "business smart" and that is a big difference. Most of the VPs I've met at Microsoft were very good technically, but tremendously bad in business and leadership.
Chris can make you believe in a vision without bullshitting you. When he talked at meetings and presentations people would listen. He was (is) very open to critic and feedback, which is a rare thing. Most execs and managers say they are, but they will get back at you if you say something that is not aligned with their beliefs.
Why this is not a big surprise?
When Chris came back to Microsoft he told me the reason was that Amazon was not exciting as the software business was and that he missed the rush of shipping software (not 'shipping' as in 'package shipping' ).
I guess that he just saw a window of opportunity with so much happening today. I'm sure he will be flooded with offers to join existing VC-funded startups, but he is unlikely to do that. The same way I was unlikely to join any company, for any offer once I decided to start Sampa.