Byron,
Just to add a further point which might make it easier to visualize.
If you connect a load across two conductors, current will flow if there is any difference in potential between them.
It doesn't matter if one wire is grounded and the other at some positive or negative voltage with respect to ground, or whether one wire is positive to ground and the other negative.
In fact you will still get current to flow if both wires are positive to respect to ground or both are negative with respect to ground, so long as there is a difference in potential between them.
Electrons will flow from whichever wire is the more negative to the other wire. It doesn't matter where the ground connection is applied.
With AC, the polarity is changing (120 times per second in the case of a standard U.S. supply), so the current does indeed flow in both directions alternately -- Hence the name alternating current.
[This message has been edited by pauluk (edited 11-08-2003).]
