Sadly, I have just backed up my iTunes, and in the process, discovered that my original iTunes Library.itl file was damaged, and with it, the new, duplicated, file also damaged. So I was prompted to create a new Library itl file, which of course has no playlist information.
Thus did I lose years worth of playlists, all in the course of backing up! My original media are all there, over 100GB of music, but no playlists.
So now I look forward to the 'joy' of recreating all my playlists.
Thinking hard about an alternative to iTunes. Perhaps going back to my CD collection, ha ha!
This is a very bad and fragile system. Too bad so many people are reliant on it.