Electric bicycles take several forms:

1. Pedelec: Must be pedaling for the motor to be operative.
2. No-pedals: This usually involves someone taking a bicycle frame, throwing off the pedals, and connecting the motor directly to the wheels. The user doesn't pedal but has footpegs instead.
3. The third I don't know a good name, but allows the user to pedal whenever they wish, and use the motor whenever they wish.

In my experience the pedelec is interesting because there's no throttle to deal with. It's very natural if you already know how to ride a bicycle. Plus the pedelec design forces you to exercise, and if your purpose for a bicycle includes physical fitness then the pedelec is to be preferred.

Electric bicycling discussion groups

http://sports.groups.yahoo.com/group/novalev/

http://groups.yahoo.com/group/power-assist/