I had a 3.2 Ghz P4 at the beginning of the year, with a gig of ram and a 120 Gb hardrive. Its been running linux for a while, but when the time came to get a computer for my sister, the best option I thought would be to get myself a mac and pass it on to her. I still use it occasionally (mainly for BZFlag spanned across 2 19" CRT's, she runs fedora), but I find my iBook perfectly capable of handling the rest of my life. I can even play BZFlag on it, but I'm too slow and sweaty with the trackpad (its 40 degrees Celsius mostly down here in aust).

I find the best thing about getting this iBook is now I'm hooked on learning Objective-C and Cocoa (I've always wanted to learn C), and it performs far snappier than my sisters p4 box even though its only a 1.2ghz g4 (768 megs of ram). The UI's great, and its just a pleasure to use (apart form the fact my hands are too big for the keyboard). If you had the option to get a G5 over a pc, I'd definately go for a G5, the only mac I wouldn't reccomend over a pc at the moment would be a powerbook, the iBook's are better value, and you can get a far sweeter laptop from voodoopc.com.