I just got an HTC mogul, and have to say that WM isn't nearly the horrible thing I had expected from reading these forums. I actually like using it. The user/developer base is huge compared to maemo, and there are tons and tons of apps for it that you can download. I've already customized mine and have added a slew of apps and unlocked a few features.

maemo has lots of promise, but its development is slow and requires a bit more knowledge/research to fiddle with it. I'm guessing nokia is moving to WM because its easier for the average user, and seems to be pretty much the standard business OS for smartphones/PDAs.