Stephen Downes posts a link to an article by Simon Waldman on the importance of URL (and email address) permanence to a person's online identity.
It struck home with me a bit, since, well, my weblog is rather tied into the ucalgary.ca domain. That would make things rather difficult if the situation ever changed (no, Mike - I'm not planning anything :-) I'm just saying...)
Over the years, I've changed employers a couple of times (until returning to the U of C, where my old account was reactivated after a couple years of dormancy). I've also switched ISPs a few times, so ISP-provided addresses get invalidated rather frequently. I've got my .Mac account, but that's only valid as long as I decide to keep paying the ferryman.
This also triggered something I read/heard in the last week (I forget where/how - isn't it weird how when you get so darned much information seeping into your skull, you just kinda assimilate it and forget where it came from?) where someone was comparing email addresses and URLs to the new permanent cell phone numbers in the states (cell phone numbers aren't tied to a specific carrier or vendor any more).
That would be cool for email addresses and website URLs. I suppose you could simulate that by having a personal domain, but that doesn't leverage your institutional affiliations as they evolve, either...