3) In the US, two phase power is still in use (in a form). Most homes are wired with a type of two phase power. The transformer on the street has two hot legs from a 220v 3 phase system come in, the transformer has a center tapped secondary winding, creating a neutral. The center tapped neutral provides 120v between either hot leg and ground. The hot legs in this system are still 120˚ out of phase with eachother.
The power in homes is still considered "single phase" power, despite being two legs that are oppsate (180 degrees out) of each other.
Two phase power is a whole different beast, and is non-existent for power distribution, though most stepper motors still use a sort of two phase power. If you split these phases like you do with domestic single phase, you could have four different waveforms.
Three phase power can be split into 6 separate phases, which they used to use in old mercury arc rectifiers.
The wikipedia entry seems to agree with the other information I've read on two phase: http://en.wikipedia.org/wiki/Two_phase