This is by far the most common question I get from my weekend webmaster clients.

"How can I get free traffic to my community?"

Simple. Your site is a community, you have to find people of like-minds. Where better to find members for your community, than at other communities?

Setting up profiles and being active in other social networks is not only a great way to find new members, by the hundreds. It is a great way to build backlinks. Google's (and the other major search engines) base a great deal on links TO your site from other 'related' sites.

I wont do the explanation justice. Social Networking.