I just found out that a Content Rating solution for MOSS 2007 was released to CodePlex earlier this month:
This is very cool. Now you can build sites that allow users to rate and comment on SharePoint content. For example, create an FAQ site using the Wiki template and allow users to rate the FAQs.
It's also used the in the Podcasting Kit for SharePoint so users can rate uploaded Podcasts.
The solution includes a database schema, web parts, and fields.