I personally don't have one. My friend does and swears by it. I've used it a few times for a semi extended period of time and they are really comfortable to use. Any mouse slides across it pretty well but the Magic Mouse works really well.
I'll be picking one up when I buy my Mac Mini this summer for iOS programming
3M has a "mousing surface" available on Amazon and other places. It's not a pad, but rather a flat surface with a reusable adhesive. Supposedly, the surface is optimized for best battery life. I haven't done any quantitative measuring, but it certainly seems like there has been a longer time between recharges than there was with no pad.
My old MM worked beautifully on my old bed comforter...bought a new down one and they just don't work well together. A bit disappointing. Have tried several different mousepads and I guess the fluffy down comforter just doesn't suit them as they lose their shape.
Besides tossing my new comforter what else would you suggest? I guess I need some sort of surface to use instead of a mousepad.