1) I opened Musicmatch (the iPod-installed version).

2) I plugged in my iPod.

3) iTunes automatically launched (I'd just installed it recently).

4) iTunes asked me if I'd like to register my iPod. I said yes, and did so.

5) iTunes began to update my software.

6) After what seemed like a too-short update process, I tried to view my playlists on my iPod. The songs were all completely gone. A check of my available space shows that there is literally nothing left of my playlists on the iPod. No warning messages popped up, no error messages, nothing. They're just gone.