This is the Wheelman. It's a motorized skateboard inspired by surf, skate and ski concepts. It get speeds of up to 16 - 19 mph. Originally invented in Australia, you can now buy one in the U.S.

You control the speed via a pneumatic ball held in your hand. Hey, it can't be any more complicated than surfing, right?

http://www.wheelman.com.au/products.html