I have this weird issue, searched for it all over the forums and googled it but no use.
A few weeks ago I switched to an external hard drive with my ~225gb itunes library. Ever since my iTunes startup time was extended to 4-5 minutes. I searched for a cure but couldn't find, then lately I unisntalled iTunes, re-installed and then re-created my iTunes library as described here: http://support.apple.com/kb/HT1451
Voila! My slow startup issue was gone.
Then a few days passed and I needed to sync my iPhone, that's when I realized that my re-created library didn't include my Apps, Books and Ringtones. But the files weren't removed so I added them manually. And when I did, my extremely slow startup issue came back. At first I thought it's about the apps and tried removing apps from the library (keeping the files) but it didn't work. Then I tried removing books, it didn't work either. And at last, when I tried removing ringtones, it worked like a charm. Then tried only 1 ringtone, but the problem occured again. I also tried ejecting the external drive and adding the ringtone files to the default iTunes library location, but it didn't work either.
So at the end, my ~42000 songs iTunes library opens in 10-15 seconds but when I add 1 30-second ringtone, it starts in 5 minutes. What should be causeing this? Does anyone have a clue?