One thing that the W3C road offers, that DataPortability.org lacks is
a clear member agreement that eliminates any questions about who owns
the IP in the specs.  All participants in a W3C working group must
sign the member agreement that gives ownership of contributed IP to
the W3C.  This reduces the risk of a company or individual asserting
IP rights after a spec has been released.  The W3C can release specs
with a royalty-free, irrevocable right and license to implement.

DataPortability (and APML) have an informal IP policy that leaves it
open to future IP issues.  Imagine if some DataPortability working
group member managed to get some of their intellectual property
included as part of the specification and after DP was released tried
to collect royalties. (This actually happened to the W3C VoiceXML
spec: http://www.news.com/2100-1032-5162070.html )

I don't have a strong opinion one way or another about the whether we
should join the W3C, but I do think we need a more formal approach to
intellectual property would reduce risk that the spec would be
encumbered.

The W3C member agreement is here: http://www.w3.org/2005/03/Member-Agreement

Paul