Facebook is testing a new advertising tool that, like Google's Adsense program, displays contextually relevant ads. There is a remarkable difference between Google's and Facebook's new ad program--Facebook's is in realtime.
The goal of the program would be to display relevant ads quicker--creating a better chance that the ads meet a user need and generate a click-through. The ads will be based on the actual user's activity such as status updates, wall posts, etc--but not determined by another user's comments.
Currently, the ads are being tested on 5 million Facebook users--1% of the Facebook population.