Facebook doubled its revenues in the first half of 2011 to $1.6 billion, according to an exclusive report by Reuters.

While the number itself may be eyebrow-raising, the trend certainly isn’t. Statistic after statistic captures Facebook’s growth, including comScore's finding earlier this year that Facebook accounted for 346 billion impressions in Q1 2011, nearly double the number it delivered in Q1 2010. All together it accounted for nearly one third of all display ad impressions delivered. Its market share increased 15 percentage points from 16.2% in Q1 2010.

Another report, by eMarketer, earlier this year, predicted that Facebook was on track to pass Yahoo as the No. 1 online display-ad selling company in the U.S. It forecast Facebook’s U.S. display-ad revenue will grow 80.9% to reach $2.19 billion in 2011, giving it a projected 17.7% share of the market.

Ads Versus Virtual Goods

Still, these statistics have not fully captured the full extent of Facebook’s reach into the online space — and the Reuters report is missing crucial details as well. Reuters noted it was not clear how the $1.6 billion in revenue divvied up as Facebook also gets a 30% cut of sales of virtual goods.

Certainly it was a significant amount given Zynga‘s popularity. Another eMarketer report finds that this trend, however, may be about to level off. Citing a July study from Visa-owned payment specialist PlaySpan and research firm VGMarket, it noted that medium spending on virtual goods in social games stalled in 2011. PlaySpan and VGMarket estimated that median spending in player-to-player transactions dropped to $20 in July 2011 from $50 a year earlier, and to $20 in third-party transactions from $30 in 2010.