Communications services group WPP will spend as much as $400 million on Facebook advertising this year, according to Mediapost. This would be roughly double of what WPP spent last year.

In 2010, WPP CEO Martin Sorrell wasn’t too keen on social media for advertising, suggesting that it wasn’t very useful for marketing, stating that Facebook was “not a medium that really lends itself to commercial exploitation,” as people used it for personal communication, and not for shopping.

Things have changed, and Facebook has proven to be a mainstream mode of advertising, where social proofing drives consumers. This trend is prompting WPP agencies like Ogilvy and JWT to up ad spending. Sorrell has obviously changed his views on social media from two years ago – when he’d stated, “when you look at the times that people have tried to commercially exploit it (Facebook), it’s not always failed but often failed.” And, its not only the largest corporations that are seeing success in advertising in social media. Small business are likewise reaping the rewards of Facebook marketing.

Interestingly, Facebook is now charging $700K a day to run a logout ad.