With apologies to Don for going on a slight tangent...
One item I have seen on occasion which scares the #^$&*#$& out of me are devices such as duplex receptacles and light switches which either have been, or are still being used, in mobile home construction. These devices are made all-in-one (device and cover plate as one piece). The romex wires are laid into a channel on the back of the device, where a contact "pinches" through the wire insulation to reach the conductor inside. Then this whole thing is simply attached to a hole cut in the wall. What can be more convenient than this...practically no tools involved, no box required, and works MOST of the time
. I saw a friend attempt to unplug a kitchen appliance from one of these things, whereupon the entire device, cable and all popped out of the wall into his hand
Kinda elevates the "back-stab" devices to a higher level (but I don't want to beat that dead horse any more...).
Rbiro has a good point to make about the staples and nails. It creates a situation that may not "show itself" right away, but beware...