In line with the reviews that I've read, Windows Phone 7 seems decent. Everything moved at top speed, even the browser. Speaking of which, I checked out PopSugar, and it rendered well. The browser supports pinch to zoom, as well as double-tap to zoom, and it was a much more refined and pleasant experience than the last time that I tried Android.
It didn't seem like San Francisco was turning out for Microsoft in a big way, however. Pretty much everybody I see here has either an iPhone, a Blackberry, or a Droid (pretty much in that order). So, I think the market is already fairly saturated, and will be tough for Microsoft to break in to.
But, we'll see how it goes.
-Andy.