I've recently converted after spending almost 14 years of my life/career using PCs. I've always been a Mac-hater; I despise the whole Mac "ethos", always have, but since getting into design I've become more and more curious to see what it's all about.
After spending so long with PCs and Windows, you get blind to the issues and accept it as part of the PC way-of-life - such as the side cover of the PC being off to poke around with something, or the regular formats to sort out Windows problems.
It's hard to explain why, but when using Leopard on a Mac, you simply don't get that nagging feeling that your software will crash, or you will need to do a reboot soon because resources are running low. You just *don't* get it...really quite a weird (but nice) feeling.
Plus, for development, it's like a dream - I can test in XP IE6, Vista IE7, Safari, Opera, Camino, plus Ubuntu Linux (and other flavours of Linux, eg KDE and Konqueror) and make sure my templates work across the board, all without needing a single reboot - if I'd have known I probably would have converted sooner.
You need a few days to get into the new style of workflow, but I'm already rolling now with the new features, and I know that in a coupe of months I will wonder how I ever did without them.
The only downside is that, because I work from two locations, I find myself having to lug around the Mac (and it's a 24" iMac) from place to place
Still, it's pretty easy, just two wires to plug/unplug, I just love it.
It's a lot of money to spend I know - I had to think long and hard - but so far (for me at least) it seems like money well spent.