I built an electric bicycle with a mad scientist co-worker. This bike uses a Heinzmann hubmotor (check it out at
www.estelle.de) and puts the Zap bike to shame. The Zap makes, what, 12 mph? And it draws 500 watts, if I remember correctly. It also gives no assist at higher speeds should you wish to pedal.
My buddy Steve's bike will not accelerate from a stop without input at the pedals from the rider. But it has 800 watts of assist that it delivers up to a speed of about 40 mph. Those of us who have reached such speeds on a bicycle can attest that it is faster than it sounds.
A serious tradeoff compared to a pedal-only bike is weight. Steve's bike weighs at the very least 20-25 lbs. more than it would without the assist, and the NiCad battery pack only lasts about 10 miles if he juices it constantly.
All the shortcomings of electric bicycles are magnified in electric scooters, though, because they are mechanically less efficient and because the rider can't lend much help to the motor when the battery wanes.
The coolest thing about electric bicycles is how immature the technology is right now. It's like the state of motorcycling in 1910, when all motorcycle had pedals. Any astute electrical engineer working with a bicycle mechanic can raise the technology up to a new standard.
Another interesting line of development can be found at
www.ecycle.com