What about the dramatically increased weight of electric bicycles due to the battery? Over short ranges, the fact that humans need to exercise anyway should also become important; I would think twice about a 20-mile daily commute, but I commuted 4 miles each way along the Stevens Creek Trail during the summer I spent at Google and it was a blast. (Despite the increased physical activity, I think Google was net bad for my health because I wasn't able to resist the oh-so-delicious array of desserts.)