Online communities open but limit movement

"They get to say, 'We're being the good guys on privacy,' but they are still retaining control of your personal data," Pierce said.

Some startups aren't waiting. Minggl and Zude both promise to help users aggregate data from their various networks, including MySpace and Facebook.

There are some legitimate privacy concerns.

"In many models, something becomes public once and it becomes public forever," said Dave Morin, a senior platform manager at Facebook. "We believe in giving users control. If we move too quickly we might not achieve that."

Users must agree before a third-party site can access their data, but they sometimes change their minds. Facebook and MySpace say restricting outside storage of data ensures that other sites get the latest information, whether it's an updated user photo or a revocation of consent.

Service providers also have to consider that people may agree to be friends in the specific community — not across the Web.

So with Google's and Facebook's programs, both parties have to agree to be on a third-party site before appearing on a friends list. Although that policy extends only to minors on MySpace, adults can opt out of appearing on friends lists on other sites by visiting a new online control panel.

E-mail addresses and other non-profile data are off limits under the programs, as are profiles the services have assembled behind the scenes for ad targeting.

MySpace said it is working on giving users even more privacy controls. Eventually, MySpace users will be able to specify that only photos go to site A and friends lists to site B, rather than all or nothing for a particular site. Facebook said third-party developers could build that granularity themselves, while Google was considering it.

Ultimately, users will have to decide whether they really want to mix work-related LinkedIn contacts with the party photos on Facebook.

"I don't know if people want their worlds colliding," said Rachel Happe, a research manager at IDC. "I don't think this push to share data should go too quickly."

Fred Stutzman, a University of North Carolina researcher who tracks online social networks, said users sometimes leave for other networks so they can start over.

Jim Benedetto, senior vice president for technology at MySpace, said social networks will likely open more once they sort out the technical and privacy challenges — much as AOL and CompuServe users can now send e-mail to people who use all other e-mail services. Instant-messaging services, meanwhile, remain in walled gardens even today.

Bill Washburn, whose OpenID Foundation promotes universal usernames and passwords, said social networks will come to realize that openness makes their respective services even more powerful.

They just need to work on a common approach, said Bob Bickel of Ringside Networks, a startup building tools to bridge networks.

"It's kind of a step forward and a half-step back," Bickel said. "It may take a year or two to shake all that out, but it definitely accelerates the timeline."

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