Last.fm certainly isnt the largest social network out there but they had a neat service.
I say “had” as according to the Last.fm blog they are to start charging for use of the site.
I only recently joined last.fm, mostly for its recommendation service, and i have to say i found some interesting artist but as a poor student i would not be able to, or in-point-of-fact be willing to, spend money on such a service-especially as there are many other free services available