"There's an abstract vision for data portability that everyone can agree on, but questions remain," said industry analyst Greg Sterling of Sterling Market Intelligence.

Sites like Facebook and MySpace need to keep competitive criteria in mind, so that by embracing data portability they don't risk losing their members, he said.

"Openness is great, but if it means I'm somehow disintermediated in some way and someone takes my users, then that's not as appealing," Sterling said.

The big social sites also need to be careful about protecting the privacy and security of their members as they extend their data portability implementations. This can be tricky and complicated to accomplish, since data portability by definition involves sharing and exposing member data with other Web sites, Sterling said.

At this early stage, the parties that stand to benefit most are end-users and Web site owners, not necessarily Google, MySpace and Facebook, he said.