I’ve added a five-star book rating system. The pro vote was overwhelming. If you don’t want it, don’t add the field to your catalog. I was against it, but once the feature was up I found myself obsessively rating my whole collection.
The system is technically cool. You can add stars to multiple books without leaving the catalog page. You do not need to use the “edit” pencil. There’s no “submitting,” “saving” or anything like that. Just click to add stars one by one; at five it cycles around to none again. (Loosely, the technique I’m using is called AJAX, and is very “hot.”) I’m going to be adding similar on-catalog editing soon for tags.
Your catalog may not be currently showing the ratings field. If not, go to change fields and add it.
As with tags and reviews, ratings are totally optional. If just here to catalog, more power to you.
I haven’t added stars to any statistics pages yet. I’ll do this as the data warrants it.