2010 was the year people started to sit up and take ‘social advertising’ seriously.

According to the research company, eMarketer, social network advertising will account for nearly 11% of all online ad spending in the United States by the end of this year (2011).

eMarketer predicts US marketers will spend $3.08 billion on advertising on social networking sites this year, up 55 percent from the $1.99 billion advertisers spent in 2010. They also predict that this figure will rise by a further 27.7% next year (2012) to reach nearly $4 billion.

This year’s dramatic growth in spending will account for 10.8% of the total online ad spend in the US.

Worldwide, where social network ad spending will rise 71.6% to $5.97 billion, that proportion will be somewhat lower, at 8.7%.

Not surprisingly, the company says that the biggest driver in increased ad spend is Facebook.

eMarketer predicts ad spending on Facebook will rise to $2.19 billion in the United States this year, and just over $4 billion worldwide – both more than double last year’s spend.

In contrast, eMarketer expects ad revenues at once-rival Myspace to drop to lower than $184 million in 2011, down from $288 million in 2010 and $470 million in 2009.

eMarketer principal analyst Debra Aho Williamson commented;

”2010 was the year that Facebook firmly established itself as a major force not only in social network advertising but all of online advertising, In 2011, its global presence is something multinational advertisers can’t ignore.”

If Facebook can continue to increase its global user base and boost the amount of revenue it generates per user, it could even surpass these forecasts. Facebook must continue to innovate its user experience and its ad platform.”

To find out more, look out for eMarketer’s upcoming report – “Worldwide Social Network Ad Spending: 2011 Outlook”.