A relative recently purchased a Samsung WP7 phone. I was highly skeptical until I spent a few minutes playing around with it.

The UX experience (design, speed) was about as smooth as my iPhone, smoother than Android devices I've played with.

Right now there are not enough apps for WP7 to make it interesting to me, but if MSFT can get devs in large numbers to develop for the platform, then Apple will have to watch out. Historically, MSFT is good at making programmers develop for their platform, so the next couple of years should be interesting.

EDIT: The relative bought the WP7 device because it was much cheaper than an iPhone.