If iTunes is to be good it needs to be gutted completely and built from scratch with the core features of the program in mind. It's called iTunes yet it offers tv, films, podcasts, Genius, and not to mention a fricking social network.. Even if that doesn't affect performance it will certainly affect usability. Take a leaf out of Spotify's book, you search for music, you play music, you can add it to a playlist, that's it. And it has a kick ass UI (hey Apple, if you're going to randomly change the iTunes UI so it's inconsistent with the rest of OS X at least make it look good).