Hi John,
Its not that straight forward for us; we have to chose the lesser of two evils to restore the ratings.
I have a copy of the itunes library on a Time Machine backup although work has been done on the library since the upgrade to itunes 11 so I can't restore and get back to clean completely.
I also have a clean copy on an external disc (I do this at month end every month and put it in the safe deposit box) so I know I can get back to prior to itunes 11 and just have to recreate activity since then.
This is really my husbands "baby". He does a music blog "the perfect ipod collection" and has over 9500 individually chosen, recorded or purchsed and rated songs. He's been doing this and blogging about the top artists and their songs that make up what he considers the perfect ipod collection since early 2009. We discovered the problem because I created a playlist for my gym workouts in his collection to load just that playlist onto my workout itty ipod. We noticed the ratings problem shortly I finished my playlist and coincidently, it was only for about 1/2 the songs that I moved into the playlist. So I have set out to figure out what is wrong and exonerate myself from messing up his "baby". Keep in mind, I am the more techie of the two of us.
So at this point, our choice is to just manually correct the songs having the "old" version up on the laptop and the "new, wrong" version up on the desktop while we correct. It really goes fast with two people doing it.
I am reluctant to go thru all the work, however, until I know it isn't going to just throw out more incorrect ratings again. I haven't found anyone that has been able to absolutely isolate the trigger. Have you?
Cheryl