Blizzard have announced that they're going to be integrating Facebook support into Battle.net:

Blizzard Entertainment, Inc. announced today that its Battle.net® gaming service will integrate with Facebook®, linking the world's premier online gaming platform with the world's most popular social platform. The first step in the integration will enable StarCraft  II : Wings of Liberty  players to quickly add Blizzard gamers who are friends on Facebook to their Battle.net friend lists, facilitating their social gaming experience on the service.
"We're pleased to be working with Facebook to integrate their platform with Battle.net to enhance the social-entertainment experience for our players," said Paul Sams, chief operating officer of Blizzard Entertainment. "This new functionality will make it easier than ever to connect with friends on Battle.net and play StarCraft II and future Blizzard Entertainment games together."
Links : Blizzard