Often times in my line of work I come across forums such as netbuilders and to gain a concise idea of what the users of that forum know about social networking, I usually ask the question (what social networks do you use?).... 90% of the responses I get are (myspace / facebook / twitter).
All I have to say is... the world is much bigger than that. Sure, myspace twitter and facebook are gigantic virtually unlimited wells of money, but they are so big in fact that for most social network marketers, they eclipse the rest of the Social Network bubble. What most online marketers (especially those new to the game) miss is that there are TENS of thousands of social networks. Some might be small fish and to most they would seem "not worth my time", but often times these networks are the most receptive to user / user interaction, and much more likely to follow an outbound link than say a myspace user.
These niche networks, while alone they are small, together have tremendous reach. Just do a little research yourself and look for "basketball social network" or "mental health social network" etc. As an internet marketer, it would be a bad idea to ignore the "small fish" networks where there will be little to no competition.
Before it used to be a problem to add friends on these smaller networks, but now, universal friend adder softwares such as webDOMinator can help to ease the social network marketing burden and give online marketers reach into the niche networks. Niche networks truly are the diamonds in the rough for the online marketer.
What other social networks do you use besides facebook / twitter / myspace?