We may now better understand how social sites like Facebook and Twitter grew so blisteringly fast last year: baby boomers finally decided they wanted to network too.

The latest report from eMarketer, entitled Boomers and Social Media, takes a close look at usage of social networking sites across multiple generations: Millenials (aged 14-26), Generation X (27-43), Boomers (44-62), and Matures (63-75). While the report shows that Millenials and Generation X users have maintained their social media profiles at consistently high levels over the past three years, the number of Boomers and Matures who actively maintain their profiles saw massive growth in 2009.

Whereas only 31% of Boomers and 14% of Matures actively tended their networks in 2008, those percentages had jumped to 46% and 36%, respectively, in 2009.

As expected, Facebook is the primary social network used by boomers, according to data from both comScore and Anderson analytics. After Facebook comes MySpace, which appears to be more popular with younger users. After those two come Twitter and LinkedIn.

"Creating and renewing personal connections online is the biggest draw for these boomers," said Lisa E. Phillips, eMarketer senior analyst and author of the new report, Boomers and Social Media. "Boomers expect that technology will help them live longer and better lives and keep them connected to family, friends, co-workers and, eventually, healthcare providers."

I can personally attest to the fact that the hope for maintaining connections draws boomers. It seems like at least once a month my mom tells me about how she has reconnected with a long lost friend from her small hometown in Nicaragua or from her high school days in Indiana, all thanks to the power of social networking.

When it comes to social media sites, usage has something of a snowball effect on the site. The more people using one site, the more likely that others will use that site because it will be likelier to have more of their friends and family registered there.