I moved from Winamp to iTunes quite a few years ago, though I can't say I haven't looked back. From what I can tell Winamp is just as capable of organizing music and playlists as iTunes currently is (which is to say, a lot more capable than it was when I used it - it used to be a total clusterfuck). iTunes is nice when it works, but a piece of ass when it doesn't (people say Apple products are more stable, I say they just don't give any error feedback when they fuck up). And the constant update notifications are annoying as fuck, especially when last I checked the auto updater is complete ass (update from 10.4.6 to 10.4.7 you say? how about fuck you redownload and reinstall the entire thing because dicks). It probably isn't a big deal for one computer, but when you need to have the same version on about 5 computers for everything to stay working it's a chore to update them all.
I'd probably make the switch back if I didn't have a consolidated, networked library of music and playlists that I'm not sure will easily transfer over, as well as the issue of other people freaking out and being completely unable to adapt to a slight layout change. I'll have to look into whether it can import iTunes libraries and has good support for iDevice sync. Last I checked, Winamp really whips the llama's ass...that's something you just don't get with iTunes.
edit: Unfortunately Winamp appears to still have a fairly crap UI. I love all the features but if it's this hard to use then balls to it for now. Maybe in another 5 years.