I've had very limited experience with Macs over the years, but I do know that, while taking a class in a room filled with OSX (not sure of the exact version) machines a year or two ago, there were some fundamental UI traits that just seemed plain counter-intuitive. For instance, take the Close button. On just about every OS I've ever used, that little X in the upper-right corner translates to "end program." It's worked like that on Windows since 3.1 (or at least 95), it works like that on Solaris, and it works like that on at least two distros of Linux that I've used (Fedora and Knoppix). And yet, when I click that friendly X button in OSX...it closes the window, not the entire program. No, to close the entire program, I'd have to go up to that annoyingly ever-present menu bar and select from a drop-down list. Sense it does not make.
Sure, this is a very tiny anecdote, but I'm kind of the opinion that, if an OS can't even manage to do the close window thing right, I don't have much of an impetus to explore it further.