If you haven't heard, there is something called "social network marketing" now, basically using (hopefully not abusing) social networking sites such as Facebook and MySpace to make noise about you, your services, etc.
With so many SN sites out there, where is your time and effort best spend? Comes Obama. He's probably not spending all his time updating his SN profiles and interacting with SN friends, but his election team certainly is. It seems to have worked for him (he got elected) so maybe it can work for us, normal folks. If you head to barackobama.com, you'll see a list of "elsewhere" sites, like this:
I would think that the right column is a little too specific, but the left column could probably be considered as a must-have for any online presence, regardless of geo location or niche interests. Do you have (and actively use your) profiles on all of these sites?