After seeing this thread I went and did a refs=0 search myself. It turned up about a dozen playlists that it said were orphaned. They were all duplicates of playlists that were visible in the playlists view so I have to admit I didn't trust it at first. So I then carefully went through and checked the FIDS of these orphans against the duplicates in the playlists view. Sure enough they were different, the were duplicated playlists.

I deleted the offending duplicates and did a refs=0 search again. It now showed up all the tunes that had been in the orphaned playlists. I checked the FIDS again to make sure it was safe to delete them, it was so I deleted them, freeing up a couple of hundred megs in the process.

So I learned something new today, you can have tracks that are effectively orphaned (because the playlists they are in are orphaned), that don't show up in the refs=0 search because they are still attached to their orphaned (and therefore invisible) parent playlists.