For the first time, Facebook is now the leading publisher of display ads in the U.S., according to comScore's data for the first quarter of 2010. At least when measured by the number of ad impressions -- not by revenue or profits.

Facebook's ad impressions increased steadily throughout 2009 while the numbers at other top publishers were flat or declining. This past quarter, Facebook's impressions took off, thanks to a more ad-friendly redesign and steadily increasing traffic.

In the process, Facebook blew past the long-time leading publisher: Yahoo. (Though Yahoo still generates far more revenue from its ads than Facebook.)

Follow the Chart Of The Day on Twitter: www.twitter.com/chartoftheday