I've been a long-time WM fan, and have only recently converted to an Android fanatic. Son #2 picked a WP7 phone as his upgrade instead of going with Android with son #1 and I. We also have an iPhone 4 in the house.
WM worked fine but was stale; it was clear that it had reached an end-of-life when WP7 was finally announced. iOS does what it promises, but I have a healthy dislike for its fanatically closed systems. I'd held off on switching to Android for some time, waiting for a more mature product. Froyo held that promise and when the HTC Inspire was released I bought the first one in the store -- and I love it with all my heart.
But you know what? The kid's WP7 phone is the most stable phone in our house! It never, ever crashes. It goes for weeks without being rebooted (try that on WM!). It never drops calls, never loses wifi or GPS connections (poke at Android), it doesn't lose signal when you hold it with you entire hand (yes, iPhone; talking to you) and it just plain works all the time.
I'm not a fan myself. I don't care much for the look and feel of WP7, and I don't like the closed ecosystem (ala Apple). But yeh, it sure is stable!