Facebook advertising CPM costs rose by an estimated 40% in 12 months

"Thanks to the incredible popularity of the world's social network, soon-to-be-publicly-traded Facebook is top of mind for advertisers both large and small, many of which have been pouring more money into Facebook advertising campaigns.
But how are those Facebook ad campaigns treating advertisers?
According to ad agency TBG Digital, which looked at several hundred billion impressions across campaigns for more than 200 clients, the cost for a thousand impressions on Facebook has increased substantially (41%) in the past year, but over the past quarter, click-through rates have dropped by nearly double digits (8%). Ads sold on a CPC basis have also risen in price during the same period."

Source:  Econsultancy, 16th April 2012