I've never heard of anyone being able to send mail to a person using only their name on an envelope.
You would have a unique "ID" which you can assign to any physical address. This is all you ever give out. If you move, you update one record, and your mail will come to the right place.
I see what you are saying and I like it a lot. I think you would still need a way to have people discover the current state you live in. One thing that comes to mind is taxes that differ per state. If I told amazon to ship my package to bob@foo.bar they would still need to know where I live.
You give Amazon your ID number. They do a lookup on the ID when you place an order to receive the current mailing address. It would apply to everything, so you give all of your friends and family your mailing ID. Anytime they want to send you something, they run a lookup on the ID (enter it into a website) and get your current address.
It's similar to a website. If HN moves to another server, everyone doesn't have to update their bookmarks to point to a new IP address. Instead, they visit the same URL as always, and it automatically sends everyone to the new IP.
I think it would only work if the USPTO was in on it, instead of forcing everyone to look up the address. It should still be publicly available (for the Amazon case, and such), but not required just to send something.
Interestingly enough a colleague of mine managed to send a post card to himself from a different country using only his email address as identifier. Of course the email address was on the form
