Anton, since 1994 I've used macs to edit images and have never found them to be anything but perfect for the job. Don't get me wrong, Photoshop on a PC is 99.9% the same (apart from the actual look) but I find that, for me, Macs just seem to be able to handle the files better when they're massive. That said, a high-end PC with a loadf of RAM will, I'm sure, be just as good.
I just think you ge a better package with a Mac and the actual useability of the hardware is what swings it for me - my MBP starts up and is redy to go in about 15 seconds and my eMac ain't that sluggish either, and that's a five-year-old machine. The same can't be said for my folks' nearly-new Dell, which obvioulsy suffers from the usual costcuttting that happens to make sure a PC hits a certain price bracket. A Mac will always cost more but everyhing is designed to work as one, not bought in because it's the right price. Buy a G5 for a few hundred of ebay and it'll run miles faster than a PC of the same age.
Plus, the new screens on MBP and iMacs are sexy as anything