While questions persist over what Facebook is really worth, the site continues to prove that it is a serious player in the advertising world. According to new data, in the first quarter of 2010, it leapt ahead of Yahoo to become the single biggest publisher of display ads on the Web.

The Internet's most popular social networking site served up 176.3 billion ads to U.S. customers in the first quarter, accounting for 16.2 percent of the total market, according to comScore figures cited in The Wall Street Journal. Yahoo and Microsoft dished up 131.6 billion and 60.2 billion ads, respectively.

One caveat: Those figures don't include ads Yahoo and Microsoft serve up through their ad networks.

Still, Facebook served more ads because people spent more time on the site, loading more pages. And it's both small and large advertisers fuelling demand for Facebook facetime, according to comScore. The obvious draw is the site's massive number of users, which now total 400 million, up from 200 million in April 2009.

The total number of ad impressions hit 1.1 trillion – up from 944 billion in the first quarter of 2009. (Get online advertising advice here)

Meanwhile, Facebook's reputation for privacy took another hit on Tuesday when news broke that a Web security consultant, George Deglin, discovered a way to harvest Facebook users' names, email addresses, their friends' email addresses and other details through the site's "instant personalization" partner, Yelp.com. "Instant personalization" is one of Facebook's newest and most controversial features.

Luckily, Deglin did not seek to profit from his discovery, unlike a Russian hacker. According to TechCrunch, Deglin contacted Yelp and Facebook, which temporarily shut down Instant Personalization to fix what Facebook called "a bug."

Editor's Note: This article was corrected to clarify how Facebook serves Facebook ads.