Because of the cost of the Earthing sheet, I needed many questions answered before I committed to buying one. I wanted to know if there was a way to have proof that the sheet was doing something. I went to Home Depot, bought a volt meter, and then ordered the sheet.
At first I was nervous about using a volt meter without too much knowledge about electricity, but I bravely figured out how to insert one lead into the ground port of the electrical outlet, and the other I held between my fingers. In this way I could measure body voltage, which ranged from 2-4 Volts depending on my location. This voltage is coming from electric wires from nearby appliances and from wires inside the walls.
When the sheet came, I lay on it and did the same test. The voltage went down to 0.1. Fantastic, it works! Electrons are doing their thing as I am connected to the ground via the Earthing cable. Turns out, sleeping this way has improved my slumber. I no longer wake up in the middle of the night and I have great energy during the day.
I made a video to give some basic explanation of how the Earthing sheet works. Let me know if you have any questions about the technology. It's pretty cool.
EDIT OCTOBER 2012: I stopped using the earthing sheet pretty soon after I tried it - about a month. I couldn't tell if it was doing anything. I was still waking up stiff. Then this month I slept on it for about a week, with the cable going into the ground port, not the ground. I had trouble sleeping that week, perhaps because of dirty electricity affecting the cable. So I can't recommend the earthing sheet right now.