Social networking is moving towards niche audience as local and special interest networks build. Hitwise looks at some interesting growth patterns for three niche groups; cafemom, eons and dailystrength.

Thanks to LeeAnn Prescott @ Hitwise.

Here's a couple more useful links;

http://www.amateurillustrator.com/ - a place for illustrators.
http://www.ning.com/ - an engine for anyone to build their own social networking site. Check out http://my.rawkus.com/ for example group.
http://www.superdeluxe.com/ - male centric network with a comedic spin.
http://jumpup.intuit.com/ - Intuit run business and innovation network.