My mac is just over a year old, so I'm a new convert.

I didn't do it because they are cool. I'm about as geeky as they come. I have built machines, administered various linux and unix systems and I write C++ code professionally. I started off as a windows fan back before windows 95. I went with the mac because of OS X. It's an amazing improvement on windows. It's as simple as that. It seems goofy, but the OS makes a huge difference in how frustrated you get with your time on the computer (or not). That is why I switched.

It's not flawless, but for me, it's simply a platform with which I can actually do stuff without having to fiddle with fixing something else first.

As for what you can't do with a mac, like folks have said, you can install windows on it and switch back and forth (or even install windows as a virtual machine). I didn't do that. The only thing I lost was xfrog, which kinda sucks. But, one of my goals is to write my own plant building software, so that is probably just more incentive to start that, lol.