craigb
dcumpian
Best reason to use iTunes: Smart Playlists.
I have not seen any other implementation that works as well as Apple's, and I have looked because I would love not to have my library be so dependent on Apple's whims.
I have playlists that auto-rotate music onto my iPhone whenever I sync using a complex set of smart playlists that take into account genre, ratings, play count, and last played date. Couldn't live without 'em (/hyperbole).
Dan
Um, as mentioned above, MediaMonkey? It's better at all iTunes features than Apple is, plus it has FAR more abilities if you need them and, if that's not enough, there are addons to cover just about anything else you may need. 
Last time I checked, MediaMonkey only partially supported what iTunes can do in regards to smart playlists, but that was a couple of years ago. I think there were some things that didn't get fed back to the library besides play counts.
If you are ever curious, there is/was a guy going by the name of "Code Monkey" who put together a very comprehensive PDF on building a smart playlist based library. It took me 3 days to build it initially, because there are so many playlists and they depend on each other to work properly. The end result is truly wonderful and I love that I never really know what's going to come up next, but that it generally will fit the mood and my favorites are sprinkled about like seasoning.
Regards,
Dan