We have talked about all sorts of concept devices and gadgets that turn up on Yanko Design. These Google Envelopes are possibly one of the most interesting concepts I have seen. It really looks like something Google would pull as an April Fool's joke. Considering the day, if this were on Google I'd be calling BS.
Since this is a design concept, I'll let it slide. The idea is that the user can get an envelope with a map printed on the outside. The return address label is in a bubble at their start of a route traced on the map envelope.
The destination is in the address bubble at the end of the route. Between the two is the route that the letter takes to get there. This is actually cool and I could see people really liking this, even if most of our communication is digital today. Basically, in the concept the user could write an email in Gmail and have it sent as a physical letter.