The post up were I am (North of Scotland) is actually really good. We've had parcels occasionally left with those next door and have taken things in for the neighbours, and every once in a while a note will come through the door saying "Left behind plant pot in garden" ect, but most of the time if we aren't in it goes back to the sorting office and you can pick it up after a couple hours.
However, even though we have never had problems with our neighbours and post (Other than not being aware anything has been delivered till they turn up with it after they've finished work) I really would rather that my post not go through them, for one simple reason; they didn't order it.
If our house has ordered it, it should be delivered to our house, and if not, taken to a secure location to be held for our collection. The post office and the postie have no idea about the nature of our relationship with the people on our road, and they should not be making assumptions that it is safe to leave parcels with them, or theirs with us.