First, there is this weird thing of programs in the */bin folders versus application structures in .app directories. The next problem is the Terminal - Even xterm is more comfortable to work with, specially when you have a three-button mouse. Then there is the less than stellar X support (I always had lots of problems piping X clients from a beefier computer to my Mac). I also dislike the fact many settings are stored not in files under /etc, but in a database. And, finally, there is no package manager (but that's not a non-Unix thing, it's more a non-Linux thing).

For those reasons, I prefer a Debian-based OS. I keep reading OpenSolaris has a nice package manager that can do rollbacks and may consider it in the future. As for OSX, it's not for me.