Well Mac OSX is a lot more system-friendly. Less processes, less processor usage. My iBook G4 will only slow down when I have an MSN client running, with firefox, with other processes running and then trying to rotate or filter a neg scan that was scanned at the highest resolution from the epson scanner/printer on my mum's windows pc (that crashes when editing the image on there). Maybe this is merely GimpShop being less Mac-friendly due to it running through the X-Window platform, but other than that my mac has never really had a problem.
I've always felt with Windows, you need your computer faster and faster just to handle the sloppy programming and bugs in the Windows OS. Remember, windows was originally built on top of DOS, and every system process with Windows takes more processor cycles than it needs to because of the architecture. I may be wrong, but I grew up with system engineers and thats pretty much how they said it to me.
EDIT: The new BootCamp on MacTel's is definitely there for non-mac users to shift from windows systems. There are a few apps that arent available or arent supported on a Mac, and you need windows for that, but yes if you're not familiar with a Mac and you're afraid to let go completely, you may want a Mac dual-booting XP and OSX