PopCap has announced that the Facebook version of its Bejeweled game, Bejeweled Blitz, has attracted more than five million monthly users.

Five million! 75 per cent of whom are female. So far, more than one billion sessions of the game have been played, too.

Not bad for your first toe-dip into social gaming. The game has been in beta on Facebook for the last six months, but launches officially today.

The game sees people playing one-minute rounds of Bejeweled - which has been a proven hit on mobile - aiming to get the highest score possible.

PopCap's chief creative officer Jason Kapalka says the idea was originally an in-joke. "Who’d think anyone would play a ‘casual’ game with such a frenzied time limit? But it turned out the one-minute timer actually made the game more accessible, as a bite-size entertainment for people busy doing other things on Facebook."

Meanwhile, PopCap's head of online and social projects John Vechey gives as good a summary of the appeal of social gaming as we've seen: "The social nature of the game felt like the missing link. Playing Bejeweled on your own was always fun, but playing with and against family and friends takes it to another level."

PopCap's announcement of the news says that it's "not providing any details" of future plans to launch Facebook versions of games like Peggle, Zuma, Bookworm, Plants vs Zombies and Chuzzle.

We're assuming this is code for 'they'll be launched as soon as we can get 'em live'.