I just signed up and received a welcome email featuring a hashed URL which refreshed to a URL including my auto-generated username:
There are two problems, though. One, there's a close parenthesis on the URL. That's probably wrong.
Two, even without the close paren, the URL says there's no user at that address. Well, that's because I changed my username to something I prefer during my signup.
It seems the long hash URL should look up my *current* username and refresh to that instead of the old one. That way, even if I change my username N times before clicking the link, the link will still work.