I wrote some code for this in 3.2 that assumes a rating is an integer from 1 to N. Like the 3.x general-comments, it assumes you want to rate an object in a table.
It only took half an hour to write so forget about admin tools or anything else fancy (ad_general_ratings_form assumes the user is already logged in, for instance) but may serve you as a starting point. I've put it up here.
