There seems to be endless places for musicians to network on the web.
The obvious places are Face Book, Myspace, and Twitter. I happen to like more specialized sites that are made specifically for musicians. I subscribe to Flatpicking Guitar magazine which also has a great social networking website where acoustic guitar players share information and music. Check this site out if you play acoustic music, plan on learning, or simply enjoy listening. Here is a link to my page, it is as good of a place as any to get started. Enjoy!