Qdos have some very nice Foaf-related apps that allow you to various things using the aggregate of foaf files they've collected.

As announced, you can search and view foaf files as nice html, validate your foaf file a service which catches some common mistakes in foaf files. There's also a social verification tool, giving you the ability the ability to find if an open id is in your network to a level of two degrees, and a reverse foaf search, which gives you a foaf file output containing the people who claim to know you; and

I was chuffed too that Mischa and Steve have also added a 'forward' lookup so you can see an RDF view of your friends, keyed off your id within a foaffile (the #me), email, mboxsha1sum, homepage or weblog. As Mischa says:

"I guess this makes our facility similar to that of the google SocialGraph API, but with an RDF flavour."

I've added a class to my tiny java library that uses the qdos forward search to find your friends.

Usage is

 sh foafuser.sh --contacts http://danbri.org/foaf.rdf#danbri

 sh foafuser.sh --contacts 01e253737c46286ff7cc1183be05ab64fea15438