You may also hear this called a 'French three way', 'Carter three way' or an 'illegal three way'. By whichever name you use, it is illegal and dangerous. The system switches the neutral, which is a clear violation of the NEC. Additionally, on one of the 'off' positions the lamp is still 'hot', with both the screw shell and the center pin 'hot' so that there is no voltage between them.
They way that it works is that you use the three way switches _fed_ from the traveller terminals, with the common terminal connected to the lamp. If one three way is switched so that its common is connected to hot, and the other three way is switched so that its common is connected to neutral, then you complete the circuit and the lamp lights. If both switches present neutral to the lamp, then the lamp is off and everything is safe. If both switches present hot to the lamp, then the lamp is off, but everything is energized to line voltage.
Take a look at
http://www.geocities.com/gary_wachs/ElectriPuzzles.html for some interesting three way circuits.
-Jon
