>OK, so your social security number is your "digital address", and the post office has a database of everyone's current address.'
No, not really, Yu-ID is not the same as the My-ID (akin to social security number). So you wont have to reveal your social security to your taxi driver etc. if that was what you worried about.
>If you move you still need to notify them, although perhaps in Japan big brother already knows you've moved.
Yes you would have to change the physical address for your Yu-ID, but you don't need to tell all your acquaintances to update their greeting-card address list ( they can still send to the same Yu-ID)
Another case might be that you are temporarily living at a 'summer-residence' , or that work takes you to a new locations for months at the time.
>So you wont have to reveal your social security to your taxi driver etc. if that was what you worried about.
Yea, but now this taxi driver will forever know where I live. Thanks, but no thanks.
So will he if you give him your ordinary address? It's good to be careful of these things, but I think you are being a little bit paranoid.
Reminds me of that old joke: Drunk man hails a cab, gets in.
"Where to?" asks the driver.
"Home!" says the man.
"Well, where do you live?"
"None of your business!"