Mac OS X only: Freeware application AutoRate analyzes your iTunes metadata and automatically rates songs based on play frequency and skip count.

If you're too indecisive to rate your tunes yourself, AutoRate is the perfect tool: cold and calculating, rating music on just on the facts. You can run AutoRate any time you want to update your current ratings, and you can limit ratings to playlists, so if you don't want AutoRate to mess with ratings you've made yourself, you can set up a smart playlist of non-rated songs and let AutoRate get you started with them. On the other hand, if you want it to constantly update your ratings, the download also comes with an Applescript that you can run regularly (see the Readme for how to set up daily, automatic rating). ? Adam Pash