Yep, those can be fun, though the older ones tend to break down, like from harddrive issues. I gave one to my friend for free about 2 years ago. Just last spring, it had two issues: the 4GB HD had died, and the motherboard had a problem, USB, I think. It wouldn't start up. Fortunately, when I got that iMac, I also got the motherboard and HD of another iMac. I did brain surgery and a board swap/HD swap and now his iMac is working fine.
I also discovered a dirty secret in the process: I remember reading sometime that the original iMac did not have fan, but when I opened it up, there indeed was a fan hidden inside!