From AdAge:
Facebook-home-page ads on average generated a 10% increase in ad recall, a 4% increase in brand awareness and a 2% increase in purchase intent among users who saw them compared with a control group with similar demographics or characteristics who didn't.
But the increase in recall jumped to 16% when ads included mentions of friends who were brand fans, and 30% when the ads coincided with a similar mention in users' news feeds. Brand awareness saw similar bumps: up 2% from just a home-page ad, 8% with a “social ad” bearing mentions of friends who were brand fans and up 13% when a home-page ad appeared along with a mention of friends who were brand fans in the users' news feeds.
via Nielsen: Facebook’s Ads Work Pretty Well – Advertising Age – Digital.