The power to your home is supplied at 240V. It is split 120V on
either
side of the neutral. The neutral is connected to the ground, but it is
not
a ground. Each 120V circuit is one one or the other side of the neutral.

Joe...
I never thought about this before, but in the 2 phase system as you
describe,
where does the transformation occur? On the pole down the street?
If so, the utility company has me and many other costumers experiencing
possible imbalances due to the communal sharing. How do they account
for these potential problems? (no pun intended)
I uinderstand your explaination, but I think in a low impedance system
as the power grid, you would need a large current difference in the 2 legs
to see anything measureable. Does it really happen in the real world?
I'm aware of brown-outs, but this isn't it..........

(and speaking of grounds, what defines a ground? That's a relative thing)