I've been using iTunes on Mac OS since the very beginning, and it's slowly become more and more unwieldy. I honestly believe that it's time to give the whole thing a serious redesign, preferably breaking it in to three separate apps.
1. Apple Media Store. The front end app store for buying all the stuff Apple so desperately wants to sell us.
2. iDevice Manager. Where we can load any media from the database(s) into the iDevice of your preference. This could also hook in to iPhoto and whatever other repositories exist in your file system.
3. iTunes. The database manager app that (shock!) just plays stuff, but does it very well and with minimum overheads.
The resources that iTunes currently needs for just playing a song is, quite frankly, daft. Apple has a perfectly adequate media player in Quicktime, but it never gets opened, just because iTunes wants to be the front end for everything.