Facebook justifies its approach as an attempt to protect user privacy. Smarr says that one clear aim of Facebook Connect's design is to make sure that users' information stays in sync with what's on Facebook. If two people dissolve their connection on Facebook, for instance, they dissolve it on any sites using Facebook Connect, too.

Smarr says that he's not surprised to see sites working to support a variety of competing offerings. "Sites like Twitter want to support whatever they can," he says. If users maintain Twitter access from other sites that they like, they can interact more with Twitter. The engineering challenge this creates, though, means that many sites have a strong incentive to push vendors to settle on common standards, Smarr adds.

"Most services will want to integrate with two or three major players for the time being," agrees Chris Saad, cofounder of the DataPortability Project, which works to make it easier for users to share data between services. "The concern is that it won't scale well." Saad says that as sites feel the pain of integrating with multiple services, and users are confused by seeing "5 or 10 or 20 ways of logging on," vendors will probably be forced to work together more.

Saad notes that in spite of Twitter's efforts to work with all the available services, there's "very strong competition" between them. "Facebook's strategy is to own the social graph," he says, explaining that, if many sites use Facebook Connect, then Facebook stays in possession of user data, and knows what its users are doing across the Internet. "Google is trying to dilute Facebook's power," he adds. Google's service would keep more social information out in the open, where it can be indexed by Google's search engines. As social networks battle for control across the wider Web, the likely short-term result is "a whole bunch of noise," Saad says. "Ultimately, though, with all these log-ins, we're still going to have the same pain. There are too many systems, too many icons, too much complexity. I think it's going to bring us back to square one."