I'm probably a bit weird, but all the computers I own now are macs... and I run windows 90% of the time on pretty much all of them. OSX really is pretty, and I like having a unix with a nice GUI, but when it comes to usability I think OSX just isn't very good. Task switching is awkward. The dock looks nice, but compared to the taskbar it's not very functional. Maximizing windows often ends up with surprising results. (Does it take up the full screen? Or does it just vertically maximize? What happens if I try to unmaximize?) Useful keyboard keys are mapped to weird things (for instance: home/end moving to the beginning/end of a document instead of the end of a line. I need to go to the end of a line about 100x more often than I need to go to the end of a document).

Also: animations. They're great for demos, but when you're trying to get serious work done they're irritating and you can't turn them off without some commandline-fu. I get the impression apple pretty much will always prioritize gloss over functionality.