Also they can be very much upgraded. After my 1 Year Applecare ran out I installed a 2.16C2D CPU out of the last 24" White iMac, 2GB RAM and a 7200 RPM Hard Drive. It really is fast and so small. Sure it has an Intel GMA950 but unless you expect it to play the latest 3D Games at high settings, it's fine for pretty much everything else.

Do remember that doing the mods I did will void the warranty. Also the reason the 2.16Ghz C2D was removed from that 24" iMac was a friend had an accident and destroyed the iMac! Poor iMac!