I use both. For years and years (since the 80's), I only used PC's (yeah, pre-Windows) and occasionally some older now-defunct systems. 2.5 years ago or so, I decided to try something new and get a Mac.
I do however, use a PC at work, and I've set up my Mac to dual-boot with Windows 7. All in all, there are still things I like more about Windows. The file manager's more to my liking, support for gaming is incomparably better, I generally like Visual Studio for programming, and there are a number of things about the Mac interface that annoy (only resizing windows in one corner, maximizing window size not filling the screen, etc.). There are also things I like more about the Mac - less worry about viruses/malware, more simplified easy-to-customize desktop, etc.
A lot of it's simply what you grew up with / get used to, I think. I'm not due to get a new system for another couple of years, and I'm not sure if I'll stick with Macs when I do. Although dual-boot is working pretty well for me now.