I have two. Well, one is an old clone, running Linux.

Basically, I think the user interface is more well thought out than Windows. Apple published books regarding UI, and Mac developers are very strict about following Apple's guidelines, thus applications feel familiar even when you run them for the first time. [note, this is true statistically, not absolutely.]

For geeks, Macs should be interesting because it's a change, w.r.t. software, hardware and development. Also, if you're into free software and stuff, MacOS X is a degree more free than Windows XP (i.e. Darwin-based), which should quiet your conscience a bit. Oh, MacOS X is also a unix, which means that you can have stuff like command line, apache, X, and all the rest of our geeky favorites.

Plus, of course, they look great.