Declared stats on Facebook UK advertising

"I guarantee CPMs [cost per thousand impressions] on our home page are three or four times those of Yahoo’s. On click-through, the engagement levels we’re getting are 10-15 times that. Not 10% more, 10-15 times Yahoo’s click-through rates. This is where we’re selling to P&G and those big brands.
The other side of our business is performance: those little square boxes, ASUs [Ad Space Units], that appear everywhere except the home page. 80% of our inventory is driven through a self-service auction model. We’re on 50bn of them a month in the UK. That’s scale. And big brands are saying they’re getting more volume and lower cost than Google on Facebook right now."
Source: Blake Chandlee, Facebook EMEA Commercial Director (& ex of Yahoo Europe), interviewed by the NMA, 10th December 2009