[kragen]

Another advantage is that you can run machine tools off a bike. The traditional Argentine knife sharpener rides a bicycle around town blowing a sort of multitonal whistle; when you take your knives downstairs to him, he puts down a stand that lifts his rear wheel off the ground, engages a belt with the rear wheel (which is modified to enable this), and drives his grinding wheel off the belt. This is a substantial advantage over the medieval method of having your apprentices whip the lathe and pull the whip.

Really, bicycles have a lot of advantages in any kind of material shortage. I've just been a bit down on them because of the amount of work they need.