iTunes is GREAT - I've been looking for something to organize my MP3 library.
However - the "Library" in iTunes is NOT just one big playlist. I moved some stuff around on my hard drive and ended up having to reimport my MP3 library into iTunes. Well, there was some mix up, so I decided to scrap the library by doing a "Select All" in the library window and hitting delete. I got a warning about moving this to the trash, and thought "Big Deal!" and hit the "Yes" key instead of cancel. Emptied the trash and Poof! Bye bye to 2 GB of MP3s.
However - I had just backed up the whole thing to my external Firewire drive, so there was no big loss.
Learn form my mistake - the MP3 library you save may be your own!