I see folk have reported such in the past and such ratings are in your library so try installing the last backup and see if it comes back. Again, many folk don't backup so they can't try it.
I updgraded my itunes (Windows XP 32 bit) from version 10 to 11 and it appears that all the ratings I assigned to my podcasts have disappeared. None of my podcasts have any ratings. Is this a known issue or might I be doing something wrong?