Some people here understand switching a light from two locations, but don't realize that you can include extra positions if you wish.

I did a complete rewire on a friend's house a year or two ago, and had his living room lights switched from three locations. He later had somebody in doing the walls, and a sheet of drywall had to be changed, so one of the 3-ways had to be disconnected temporarily. When the wall-guy put it back, he got the connections wrong so that this switch had to be in one position before the lights would work -- In the other position you couldn't turn on the lights from anywhere else.

Despite my friend telling him that the three switches had all worked fine before, this guy insisted that it wasn't possible to switch lights from three places like this and that if you had a third switch it would always have to be "on" before the others would work. [Linked Image]