I actually quite like Mac OS X. Things seem to "just work" most of the time, or at least, more of the time than they work for me on GNU/Linux. I can't give any examples off the top of my head, but it seems everything in OS X just "flows together" much nicer, and that's even including programs like Chromium which aren't from Apple.

The reason why I don't use it, however, is because it's tied to the hardware in such a way that if I want this "just works" feeling, I'd need to purchase hardware from Apple, which for me seems overpriced and it shouldn't be necessary. Further, OS X has its quirks that don't let you run it like Linux or BSD - for example, installing things like PostgreSQL.