First off, I didn't write this plugin, I was browsing CakePHP's plugin bakery and it came from there:
http://bakery.cakephp.org/articles/schneimi/2010/08/19/ajax-star-rating-plugin-1

This is an excellent plugin and very easy-to-use.  The above article is extremely detailed and provides excellent step-by-step instructions to set it up and get it running.

In reviewing the comments, like any self-made plugins there were a few issues encountered and ironed out along the way, so if you run into any issues be sure to search the comments.
Enjoy this excellent Star Rating Plugin for your next or current CakePHP site!