Yes. Barely 36 cents per-active user, per-month. 
According to Alexa, Facebook gets an average of 13 pageviews per-user per-day. According to this report each user visits Facebook an average of 40 times per-month. This would mean:
- a minimum of approx 440 billion pageviews (!) in Dec-2011 
- a maximum CPM of 60 cents per thousand page views 
Yes. Barely 60 cents CPM. On a per-impression basis this number could be 3x lower because Facebook has about 3 ads per page.
And that's the #2 website in the world. No wonder traditional publishing companies are dying everyday - not everyone can have close to a billion active users to allow a few cents per-user to cover their costs. Internet advertising is such a horrible monetization model. We have to think of something better!
 And that's the number per active-user. If we compute this for total users, the number will be much lower.
 845 monthly-active-users x 13 pageview per-user per-day x 40 visits. Not the best calculation, but good enough to give us a minimum value
 USD 3.15 billion divided by 12, to get the average monthly revenue, divided by 440 billion pageviews x 1,000. Again, I know, not the best, but good enough to give us a ballpark.