Facebook's US advertising share has fallen to 12%

"Facebook's U.S. advertising growth has slowed down to a third of what it was in 2011, according to a report issued Wednesday.
After growing at impressive rates in the 60% range during the first three quarters of 2011, Facebook's advertising growth fell by more than half to 30% in the fourth quarter, and during the first part of 2012, the growth rate went down to 21.2%, according to a report by the IDC.
The slowing growth has resulted in Facebook losing market share. After holding on to almost 14% of display advertising at the end of 2011, Facebook's share is now down to 12%.
"They're still growing, but they're not growing as fast as they should," said report author Karsten Weide, the program vice president of media and entertainment at IDC."

Source:  Data from IDC, reported by the LA Times, 27th June 2012