Alternative/underground music review webzine Pitchfork Media has an article on
file-sharing after AudioGalaxy. All the clients there (other than the one using the dead inefficient Gnutella system) are proprietary Windows-only clients, and, as they point out, not unlikely to contain spyware and other such nasties. (That's the consequence of file-sharing being driven underground; to use it, one has to truck with people of flexible ethics; much like the case with drugs.)
Though they don't mention any open-source systems, such as
the Circle.
(via Jimbob)