Yeah. The interface is decent enough now, but I have serious doubts about its ability to scale and sell apps when you have a very low density home screen where it's going to be laborious to do anything outside the highly integrated included apps.
But here's the billion dollar question, however:
How the heck does Microsoft propose to actually profit in the mobile phone business?
They have never, ever made a dime in profit on licensing WM and its predecessors, and now you've got another vendor giving away pretty good phone software with liberal licensing terms this go around, and another vendor with a very highly profitable software/hardware system, and a third vendor with a lot of enterprise lock-in.
And MS is going to make money doing this time how? Licensing this for peanuts and pimping Xbox live? Really?