Jeni is wondering about versioning URLs. A fascinating area and one I spend a bunch of time working
on for Propylon.
Jeni, I tried to add a comment to your blog but the Captcha system proved that I was a bot to its own satisfaction so I'm replying here:-)
A terribly useful concept for reasoning about URI versioning from Saul Kripke.
I have successfully applied Kripke's rigid designator concepts to some thorny document management problems - in particular legal citation. Sadly, making it work for the Web-at-large would involve centralizing some plumbing in a way that is anathema to the decentralized model of the Web.