MySpace still ruled
According to a Media Post article, MySpace ruled the U.S. social networking space in terms of sheer volume, receiving more than three-quarters of all the social networking traffic in the U.S. in 2007.
Facebook took the number two spot–snagging nearly 13% of all social net traffic, followed by Bebo with about 1%. But all you Facebook lovers should be happy because traffic to MySpace was actually down by 8% from the previous year. In contrast, traffic to Facebook was up by some 51%.
Researching age demographics for Myspace vs. Facebook provided me with no good recent reports on the age differences, though I found a great one from 2006 about how 68% of Myspace users are over 25.