Yesterday, my iTunes playlists and podcasts were intact. Today, when I turned on my computer (MacBook Pro) and launched iTunes, all my playlists and Podcasts have disappeared. As far as I know, all my songs are still there (I've got ~5000). Can anyone speculate why/how this happens? I've searched the forums and have found a few mentions of how to restore the iTunes library (from a Time Machine backup or elsewhere). However, I'm curious if anyone can speculate why this happens?