Most of the proxy servers in the world are running Squid, so you're probably looking for SquidNotes.

Peer your proxy with MetaNet users

If your proxy speaks ICP then you can configure it to use other, local caches, to retrieve data from. If you're on the MetaNet, and your metanet connection is faster than your international connection (or you pay for international traffic) you might find value in doing this. #wlug is probably a good place to ask.

What good is a proxy server if no-one uses it?

See WPAD to figure out how to make your LAN clients automatically pick up the proxy server.