Sci Am has a nice review of a $2,000 50lb LiOn battery power assist bicycle.
Recharge times are six hours. It's a pure assist system, there's no power regeneration. A computer controlled transmission system adjusts energy input.
I like this idea. It's not hard to imagine a $1,000 version in a few years better optimized for higher speeds (drop bars, recumbent design, etc.). A recumbent tricycle version with some shielding could make rain or snow conditions tolerable for the average reasonably fit person.
Development is active in Europe and China; but if our gas prices go to $8 a gallon we'll be doing development here too.
Giant has a web site view.