Years ago I remember reading somewhere on these forums though, that a 3-way is not UL listed for use as a single pole switch and thus illegal, posing a shock hazard since the unused traveler terminal becomes hot in the "off" position of the switch... on the other hand I assume anyone removing a switch cover should know enough about wiring not to touch any terminals without killing power to the circuit. I guess that's one of the classic "lawyers vs. common sense" cases
I have also heard that a 3-way cannot be used as a standard switch, but as I heard it the reasoning was that a 3-way isn't marked with the ON and OFF legends on the handle.
Of course, that reasoning falls apart with Decora switches...
