I have a yale lock and mortice lock on my front door. I figure if somebody is going to attempt to break in through my front door they can jolly well deal with two locks.
However as well as locking myself out of the house on occassion I have frequently also left the door unlocked and also left the keys in the front door (so kind of defeats the purpose). I've done that twice in this house, and once at my old house. Nothing has ever happened, but I do think how easy it would have been for some thief to rob me and stick all the swag in my car and use that to get away. I've left the car unlocked loads of times too. Unfortunately no-one has ever bothered to take the opportunity to steal it, not even in Tesco's.