dataportabilitylogo0108081.pngIn what is at least a brilliantly executed PR move, leading engineers from Google, Facebook and Plaxo have joined the Data Portability Workgroup — an effort by a number of web companies to develop best practices for sharing user data across sites and applications.

Google’s Brad FitzPatrick and Plaxo’s Joseph Smarr — two long-standing advocates of data portability — are joining. More surprising is the addition of Benjamin Ling, a former Googler who recently joined Facebook to help lead its developer platform.

Maybe Facebook will eventually let third parties fully export all of its user data, letting users do things like export their Facebook friends’ emails en masse to other applications (see our coverage of Plaxo’s back-door effort to do this on Facebook, last week).

Maybe, through this workgroup, Facebook will iron out how that feature might be implemented?

For now, though, the glass of fully portable social data is far less than half-full — Facebook is just agreeing to talk directly with these other companies about such possibilities.

Nevertheless, Marshall Kirkpatrick at ReadWriteWeb, thinks the news is a “bombshell.” Duncan Riley at Techcrunch says “this day will be remembered.”

Given the initial hype — much of which has now deflated — around Open Social, Google’s nascent social networking application programming interface, I feel compelled to stay a little more skeptical about the significance of this news until I see concrete results.

Here’s what DataPortability is up to, in a nutshell:

“[A]mong other things, [We’re] actively working to create the ‘DataPortability Reference Design’ to document the best practices for integrating existing open standards and protocols for maximum interoperability. This means users will be able to access their friends and media across all the applications, social networking sites and widgets that implement the design into their systems.”

In other words, a fuse may be lit but no bombs will go off until all of the workgroup member companies actually define and agree on standard ways of sharing data across sites. I hope these companies will, but they haven’t, yet.