Taliban:

Ratings web sites work great when the content being rated is legal (i.e. not copyrighted). The one-of-us.org site mentioned above combines content rating with a trust network. However, if users want to rate copyrighted material (like rips of music or video), a ratings website could be seen as supporting the violation of those copyrights, and thus might be shut down. Storing ratings in a decentralized system like Gnutella might be more prudent.

NiGHTSFTP:

A single database has the same problem as a single website: it's a central point of failure. Suppose we instead store copies of the ratings database on Gnutella: this helps it resist attack, but now it's unclear how to propagate updates to the database.

Perhaps what we want is a way to push the little individual ratings files around the network, and each client can grab and save the ones it cares about. So, instead of a centralized ratings database, everyone has their own local database that contains only those ratings it wants (e.g. those signed by people you trust or ratings for a particular file).