I have a huge music collection, mostly because I have very diverse musical tastes. I will give every genre of music a chance. Organizing it, however, is a bit of a pain. One day, I will tag my mp3s and make sure their album art is correct. With a 11,000 song collection, that day will probably never come. I needed a way to sort out what is actually worth tagging, and rating the music is the best way. So I began, about 4 years ago, to listen to every song I have and rating it. I spend very little time on my computer actually listening to music, and the only portable device I had capable of rating the music was a Dell Axim X51v PDA, running Windows Mobile OS. I'd sync a gig of music onto the device, then listen to the music while commuting to work, giving star ratings to each song. When that playlist became fully rated, I'd sync a new, unrated set of music.
11,000 songs will still amount to over 700 hours of music, so I'd take some shortcuts...such as allowing myself to tap Next after half the song was over (usually a 1 star).
Anyways, many hours later, my collection is finally fully rated. I knew leading up to this that I was going to face one critical problem - my music was only rated in Windows Media Player, but my Android device had no way of syncing ratings to it. I certainly wasn't going to lug around two devices just to listen to music, so I needed a way to get my ratings over from WMP over to iTunes so I can use the iSyncr app to sync to Android.
After much searching for a solution, I came across Orzeszek Ratings, which promises to get ratings from one platform to another. Hooray! It worked wonderfully, and now I had ratings in both music management systems. However, I now had a different problem - I still use WMP as my player of choice at home for its ability to share the library with other DLNA devices. I might update ratings in iTunes with iSyncr, so I also needed to be able to sync back to WMP, but if I had updated some ratings in WMP (for different songs), the one-way sync of Orzeszek Ratings would overwrite them with the iTunes ratings. Fortunately, the developer of Orzeszek Ratings has made his software open sourced, meaning I've been able to crack it open and put in a two-way sync feature, which I've been using a few months. Details are here.