I used a Mac for just over a year. There were things I really loved (UNIX behind the scenes, power mgmt on my laptop) but for the most part the UI for OS X drove me nuts and the mouse/keyboard sucked. I think I agree with just about every single point Cédric Beust made in his post on his experiences with switching to a Mac.
I’ve been Mac free for about 10 months, and Windows free for 7 weeks. I’ve got new problems with Ubuntu that I never had with OS X or Win XP but I don’t see myself going back to either any time in the near future.