Personally, I don't really like the looks of iMacs. But that just my opinion. What with iMac's is that you never can fit any powerful Graphic-Card into them, so even if it had DX10/9 support, you just can get a good card into it (8800 GT/GTX/Ultra). And other then that, they're overpriced. They've got good CPU's though. Intel is doing great lately and switching from AMD has been a great step from apple.
If you like the looks, don't mind (or like) Mac OS and aren't planing to use it for gaming and don't think you're going to be using those app's that only work on Windows, have had it with MS and don't mind paying a bit more for for having the apple logo and the 'Mac look' then you could consider getting a iMac.
Though in my opinion XP is better then Mac OS.. but then, that's an opinion.