Walmart bought 50 million mobile ad impressions on Facebook in 72 hours

"Over the next 72 hours Facebook and Wal-Mart rolled out the social network's biggest mobile-advertising campaign ever, consisting of 50 million ads. Wal-Mart's discounted deals on toys and televisions popped up in the Facebook mobile news feeds of tens of millions of people.
Unlike previous campaigns, for which companies paid Facebook only after users saw their ads, Wal-Mart prepurchased the ads and edged out other retailers for space during the all-important kickoff to the holiday shopping season.
Facebook now is considering making the option available to other companies.
Wal-Mart's results from the Facebook advertising push ended up mixed. While Mr. Quinn said he "never saw this level of engagement" before with a digital-ad campaign, which attracted more than 100,000 comments, the retailer's Facebook page also was littered with comments from users complaining about unwanted ads, among other things.
Overall, Wal-Mart said it bought two billion ads on Facebook this holiday season, three times more than last year, but declined to say what it spent. Wal-Mart also declines to say how much of its $2.3 billion annual ad budget is spent on social media."

Source:  Wall Street Journal, 16th December 2012