What's actually wrong with Windows Phone other than it came from MS? From what I've seen of it, its a well designed well executed mobile OS. You can't really say the same of the recent blackberry os releases.
Because that's just one more smartphone OS that will never support app development from anything other than their own creator's platform, i.e. Windows and Visual Studio or Mac OS X and Xcode. The world doesn't need this horrible, closed-system, innovation killing, walled gardens crap anymore.
My girlfriend got a windows phone recently, by far its one of the best mobile operating systems I have ever used. She's hates computers and loves the phone. Microsoft did a good job on the OS.