I recently re-installed Panther on my shiny new 300GB hard drive. iTunes used to load all my songs ( about 1700 or so) with one bounce. Soon after, it would take about seven to eight bounces to launch, with nothing else going on in the system. I figured it out to be the smart playlists. I had one for each of my soundtracks and albums (about 38), and two for my MP3s and AAC files. I turned these into regular playlists (I guess I will manually update the AAC/MP3 ones later on). After doing this for all my playlists, my iTunes returned to launching after one bounce. I guess the Smart Playlists search your library on startup of iTunes, and add the necessary files to each playlist. So if you're like me and are really peeved about iTunes sudden lackluster performance, try turning your smart playlists into regular ones.
I just hope, that with this enhancement going on system-wide in Tiger, Apple revamps this behavior so all our apps don't go boat slow.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040705010130758