Half of Facebook's more than 500m users play games on the network, accounting for 40% of Facebook usage, according to Playdom CEO John Pleasants, who cites his own sources. His comments may go some way to justifying the multimillion-dollar acquisitions taking place in the social gaming industry at the moment, and will add to speculation about a potential multibillion-dollar IPO by the market's biggest player, Zynga.

Social networking, in which Facebook is the dominant player, accounts for a quarter of all internet use. Facebook is the third most popular website globally, and US users spend far more time on the network than on any other web property. If social games account for 40% of this usage, it suggests they are helping drive the expansion of social networking and are responsible for a large portion of total internet use.

Playdom, which Disney acquired last month, is the third largest social gaming firm on Facebook after Playfish and Zynga. Pleasants told the TechCrunch Social Currency Crunchup that the deal breaks down into a USD563.2m initial payment, followed by an earn-out of up to USD200m.

Following the Disney acquisition, Playdom said it has become the latest firm to agree to exclusively use Facebook's Credits virtual currency system for virtual goods transactions for the next five years. The Facebook deal mirrors similar agreements signed by Zynga and Crowdstar. Virtual goods transactions are thought to account for the vast majority of revenues earned by social gaming firms. Facebook will take a 30% cut from the currency.