If you could improve one component on a bicycle, what would it be?

I might like to see a truly functional continuously variable automatic transmission. You could "set" it and ride with the same amount of effort up and down hills all day. Maybe an override could allow you to sprint or climb hills more quickly or just ride faster. I see it as having the benefits of "click shifting" without the drawback of continuously adding rear cogs and narrower chains. What do you think?

Anybody have other ideas?