@Brain_In_a_Jar: "Nice try, but I think such a model would require a magnetic monopole at a point in the centre and another one distributed around the circumference - there's no return path possible for a radial field in a flat plane. When you're done with that, you can then explain how gravity fits your ludicrous model, and thus why your disc world doesn't immediately collapse into a spheroid under that gravitational force."
Actually, having spent a while browsing the official Flat Earth Society forum a while back, I came across answers to all sorts of questions like that in the FAQ section.
Gravity, you see, is an illusion caused by the constant upward motion of the disc of the earth, which - if I recall correctly - is also necessarily accelerating constantly at the rate of 9.8m/s^2. But of course, the sun and the moon (small discs hovering above the rim of the earth, emitting light at specific times of day) do have a gravitational pull (thus explaining why gravity varies with altitude), and this can apparently be inferred from the fact that snakes are neither cats nor dogs.
The south pole, incidentally, consists of a vast "ice wall" covering the entire circumference of the earth, so the water doesn't all fall off the edge.
I do suggest reading the forum, and particularly the FAQ pinned under "Questions and Clarification". It's quite entertaining.