Squid is a high-performance proxy caching server for web clients, supporting FTP, gopher, and HTTP data objects.
I use squid at home and have in the past run reasonable sized installations as part of past employment.
I am interested in squid's interaction with cisco routers - particularly WCCP, as, in my day job I am a network engineer. So squid's network capabilities are of interest as I can tie in what I do at work with what I play with at home.
At home I regularly run Squid-3 as well as Squid-2.5 from CVS and submit bug reports as I find problems.
I have written a document on getting squid to work with WCCP here.