Social networks worldwide are estimated to bring in $3.3 billion in advertising dollars this year, according to updated estimates by eMarketer. That number represents a 31 percent increase from 2009's $2.5 billion. A full 39 percent of that amount, or $1.3 billion, will go to Facebook.

In the U.S., social ad spending is estimated to rise 20 percent to $1.7 billion. Facebook is gobbling up even more market share in the U.S. It is expected to make up 50 percent of that amount ($835 million), compared to a 36 percent share last year (when it’s U.S. advertising revenues were estimated to be $500 million out of a total of $1.4 billion).

The big market share loser in social ads this year is MySpace, whose share is estimated to drop from 32 percent in 2009 ($445 million) to 19 percent in 2010 ($323 million). Social games and apps, interestingly, are also expected to pretty much stay flat in terms of ad revenues, with $142 million of the total this year. The social game segmentation really doesn’t make sense to me. It kind of makes me wonder whether the folks at eMarketer have ever heard of Zynga.