"In 2011, Zynga accounted for approximately 12% of our revenue, which amount was comprised of revenue derived from payments processing fees related to Zynga’s sales of virtual goods and from direct advertising purchased by Zynga. Additionally, Zynga’s apps generate a significant number of pages on which we display ads from other advertisers."
It appears they would still be profitable without Zynga.
Are those ads counted toward the 12% statistic?
Is it reasonable to conclude that Zynga constitutes 80% of FB's credit ecosystem?
"In 2011, Zynga accounted for approximately 12% of our revenue, which amount was comprised of revenue derived from payments processing fees related to Zynga’s sales of virtual goods and from direct advertising purchased by Zynga. Additionally, Zynga’s apps generate a significant number of pages on which we display ads from other advertisers."
For example, if an advertiser pays Zynga to put a banner ad in their application or above the Flash widget containing their game, Facebook doesn't see a penny of that.
Zynga pays Facebook to advertiser in the right-hand column, though. Lots.
Additionally (and this doesn't count towards advertising revenue), Facebook Credits are mandatory for all games on the Facebook Platform, and Facebook takes a 30% cut any time a player purchases some.
That assumes many of those Zynga users would still be on, or use Facebook as often, if it wasn't for Zynga or other games on the platform. The significant amounts of time spent on Facebook is due in large part to games and photos. That length of time on the platform helps to drive display ad revenue.