MySpace, Facebook, LinkedIn, YouTube, Digg–people are tired of entering the same information over and over again, every time they join a new social-networking site. Earlier this year, many social-site operators announced efforts to solve the problem by creating tools that make users’ information portable. But as these products have started to roll out in the past few weeks, trying to keep up with them all has saddled websites with extra engineering.

Google announced Monday that people would be able to use its Friend Connect service to export data to the popular microblogging service Twitter. But according to a post by Twitter cofounder Biz Stone on the company’s official blog, Twitter plans to play nice with several networks: Google, Facebook, and MySpace. The post notes, however, that enabling interoperability with all three services will require a “significant development effort on our [Twitter’s] part.” Nor does the post say when that effort is likely to be complete.

Both Friend Connect and the competing Facebook Connect promise to let webmasters add social features without having to build their own networks, and to allow users to log in to multiple sites with existing passwords. And like MySpace’s planned service, they need to share necessary information between sites without violating the user’s privacy or the site’s intellectual property, and keep information across sites in sync. But Facebook’s offering, which is designed to hang on to the social data that the company has already collected, is in sharp contrast to Google’s effort to keep information freely available.

Facebook Connect lets users access Facebook services from other websites–adding new friends, writing status updates, posting notes, and the like–but all that information stays on Facebook’s network. Google Friend Connect, on the other hand, lets users interact with services from any participating site–Twitter, Plaxo, or Orkut, for example.

Companies that don’t want to give preferential treatment to either approach will likely face daunting engineering tasks for the foreseeable future. For besides embodying different philosophies, Friend Connect and Facebook Connect are fairly different technically, explains Web-standards advocate Joseph Smarr, chief platform architect at Plaxo, a company that helps people synchronize data between a variety of online and offline services.

Smarr has designed Plaxo to be compatible with both services and is working to make it compatible with MySpace as well. But while MySpace and Google are mostly relying on emerging standards to accomplish these tasks, Facebook has built its own proprietary technologies. As a consequence, supporting Facebook Connect on a site is an entirely separate engineering task from supporting Friend Connect, Smarr says.

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.”