The brawn of Facebook, the brains of Twitter

If you were a social-networking site other than Facebook or Twitter, you were probably struggling to stay above water in 2009. But if you were one of the many services built on top of Facebook's or Twitter's platforms, this may well have been a very good year.

Some formerly big names in social networking were attempting to revamp, rebrand, or recover. MySpace hired former Facebook exec Owen Van Natta to spearhead a turnaround for the News Corp.-owned social site as it saw its traffic increasingly eaten up by Facebook's; at year's end, it was still struggling to reinvent itself as a music and pop-culture powerhouse. Friendster, long past popularity in the U.S., took advantage of Asian traffic and sold itself to a Malaysian company in December. AOL, under the new auspices of CEO Tim Armstrong, more or less attempted to sweep its embarrassingly pricey $850 million acquisition of social site Bebo under the rug, placing it in a new division called "AOL Ventures."

Facebook, however, was riding high. Shortly after the start of the year, Facebook CEO Mark Zuckerberg--several months away from his 25th birthday--posted an entry on the company blog in which he announced that the social network had hit the milestone of 150 million members. At the beginning of December, it had more than doubled, reaching 350 million.