I want to be able to order stuff online from random eBay sellers, but I don't want to give out my home address -- both because I don't want people knowing where I live, and because I don't want sellers to be able to send me junk mail in the future.
To solve this, the post office (or a private company) could offer time-limited unique addresses that would redirect to my real address. When I want to place an order, I'd go to the PO web site and ask it to generate an address, which'd include a unique ID that's only valid for the period I select (perhaps a month for most orders).
Obvious problems: you can't use the address for credit card validation any more (without the collaboration of the credit card companies), and sellers generally don't like shipping to non-real addresses since it makes it harder to track down abusive buyers. It'd need regulating like an escrow service to make it workable.