Battle.net will be adding Facebook-integration to their service in the near future. The first step is to add a feature will Starcraft II-players will quickly be able to put their Facebook friends that also are members on Battle.net to their Starcraft-friends list. The function will be beta tested together with the regular Starcraft II-beta.
As Battle.net will be used for all current and former Blizzard-games, the integration with Facebook will certainly not end here. We'll just have to see how it gets integrated with World of Warcraft, for example.