As cyn mentioned, mp3s load on to an iPod just fine. No conversion necessary. You don't have to use iTunes, either. There are plenty of third-party freeware programs out there to choose from.
I love my iPod. I have a 30GB Classic (actual capacity reads as 27.8GB). As of right now, I have 3,446 songs on it, with 9GB of space remaining. I could definitely put more music on it, but I've been lazy.
I enjoy the fact that I can walk around with the entire U2 backcatalog in my pocket...as well as several other complete collections.
I really want a 160GB Classic so that I'd have room for videos too.