Today, I noticed that a playlist I'd been working on was empty. I had spent hours creating it, listening to songs for word content, and created a list of around 350 songs. They were all gone. Unfortunately, my last backup did not include this work, so it was all lost (lesson to me: backup after doing significant work). Note: all playlists were empty, but there was only one I was concerned with.
Anyway, I figured maybe it was an old version of MJ (version 293 I think), so I downloaded the latest, v 318.
Everything was going along OK. I added a few songs to my playlist, and was listening to music. I was running Replay Gain on about 60 new songs. I've been having some system overheating/crashing problems, and a crash decided to occur while running Replay Gain. After the reboot, I found that once again, my playlists were all empty. This included the one I'd just added to, the playing now list, and the recently imported list.
Sounds like there's a problem with losing data during a crash. Even if this issue is fixed, I'd like to see something along the lines of having an automatic backup (.bak) of each file that will take you back to the most recent version just in case something bad or unexpected happens.