At the first WS-Addressing f2f and Gudge said that the uuid uri scheme doesn't exist. For all the times that we have written uuid:blah-blah-blah-blah, we are just plain wrong.
My first thought was, no way! He's gotta be wrong. So I looked. Well, as the old saw says "Gudge is right". Kind of. The scheme does not show up in the IANA registry of schemes. There was a 1997 IETF Internet Draft on UUID URIs, since obsoleted.
There isn't urn:uuid name defined in the urn namespaces registry. I did find on the URI NID status page that urn:uuid had been requested but apparently no answer yet. This has been revised to http://ietfreport.isoc.org/ids/draft-mealling-uuid-urn-03.txt
Obviously this doesn't matter that much. Nothing breaks because there isn't a formal definition. There seems to be an implicit registration. And I betcha that any uuid scheme registration that differed from the implicit uuid scheme would be rejected.
I learn something new every day. Actually, I learned 2 things today. Paul Hoffman gave me the mealling draft uri and correct my terminology.