I'm having this same problem with iTunes 10.7, and I sent Feedback about it. I was able to restore most of my song metadata using Time Machine, but I lost a couple hours and I had to terminate iTunes Match on my Mac.
These methods posted above to fix the problem are fine for more advanced users, but for noobs like me it's more risk and hassle than the service is worth (which is a shame).
Seems like Apple could at least put in some simple progress alerts that say things like "iTunes Match has detected conflicting metadata on your devices, which one has the data you want to keep?" (ditto for the artwork issue in other discussion threads).
If I get brave enough to try the solutions above (and many thanks to all the contributors who posted them!) I will check back here first, and then backup, and then report results here…