Motorized Rollerblades are becoming increasingly popular across the globe. They started out entirely for sport, but with the alternative-energy movement, many people are using them to make their daily commutes.
Typical powered inline skates can move up to 20 mph and have a range of 15 to 20 miles. If you run out of power, you still have a usable pair of skates.
Commercial motorized Rollerblades cost hundreds of dollars, but with some basic equipment and a few hours to spare, you can make your own lightweight version. For simplicity's sake, only one wheel on the skates will be battery powered.
I saw one version where the user had a gasoline motor back pack with a flex cable to one boot.
I have no use for gadgets that make my feet go faster than the rest of my body. My elbows and hips hurt just looking at the picture!