At the bottom of the top five was AOL.
See the chart on Business Insider.
So how has this translated into advertising revenue market share?
Facebook's ad revenue share was $1.86 billion for 2010 according to eMarketer, accounting for 5 percent of all online spend in 2010, and expected to grow to 8% in 2011.
Some predict Facebook's revenue to top between $4-6 billion in 2011.
Yahoo's front-runner, Twitter expects to rake in $150 million in 2011, while AOL's revenues plummet, and show no signs of letting up.