Yesterday the IETF announced that draft-saintandre-xmpp-urn has been approved by the IESG for publication as an informational RFC. What this means for us is that the XSF (specifically the XMPP Registrar) will control its own "tree" of Uniform Resource Names to issue for use in XMPP Extension Protocols, as specified in Section 4 of XEP-0053. This is good because URNs are more stable than the URIs (such as "http://jabber.org/protocol/muc") that we've been using for XML namespaces in our protocols. Although we lose the ability to copy and paste such a URI into a browser and find information about the relevant protocol, it's easy enough to search for a string like "urn:xmpp:chatneg" and find the relevant specification. So the slight loss in convenience is offset by the improved permanence of our XML namespaces. Besides, all the other standards development organizations are using URNs, so why not us? :-)
UPDATE 2007-04-28: This document has now been published as RFC 4854.