For the Q1 of 2010, Facebook has become the number one publisher for display ads according to ComScore.
Facebook ran 176.3 billion display ads on its website for the first quarter of 2010. This is 16.2% of the display ad market share.Yahoo was second with 131.6 billion display ads.
This will certainly increase the attractiveness of Facebook as an advertising platform--especially when coupled with the fact that users spend more time on Facebook than any other social network.