In a recent article, eMarketer cites research by Anderson Analytics that indicates the majority of social networkers by generational cohort use Facebook, while a minority use Twitter and LinkedIn. Moreover, a majority of users younger than age 45 also use MySpace, apparently in conjunction with Facebook.
The summary data above speaks for itself. The generational age groupings were as follows: generation Z (ages 13-14); generation Y (ages 15-29); generation X (ages 30-44); baby boomers (ages 45-65); and the WWII generation (older than age 65). Again, Facebook appears to be in the lead, at least for now.