We've had a strange phenomenon ever since we moved into our house that's never really occurred for us before. We've been getting other people's mail! It seems to happen on a fairly regular basis, too. We've gotten it from as far away as a couple of blocks (with an entirely different street!). When we get it, we kindly return it to the people, in person, or dropped in their mailbox. The other day, though, it occurred to me that I don't know if we're losing mail and anyone is bringing it back to us … though once, we found our box of checks in there between mail drops, so I assume that was someone dropping it off and hopefully it isn't an isolated incident! 
That fellow on the left, in case you don't know, is Postman Pat, of the BBC Kids TV series. It's been awfully quiet in the blogosphere lately. What's everyone up to?
It happens at my house too. Carelessness is what I chalk it up too. Pft. I've noticed the quiet too.
It happens at our house too. I was thinking the same thing-I hope people return our mail!