Let me start by saying that I firmly believe that while driving a motor vehicle is a privilege which is appropriate to regulate via a license, and riding a bicycle is a right which should not have any more restrictions placed upon it than walking (or farting as Rodimus_Prime suggests). I also agree with the many posters here that a system for registering bicycles is impractical and would almost certainly cost more to administer than it could reasonably be expected to return in revenue, BUT....

I am also a strong advocate for educating cyclists, and some sort of a system which allowed for an incentive for a cyclist to become educated in the rules of the road would be a good thing. If there could be some sort of license which a cyclist could obtain which might require showing that they understood the rules of the road, and which could be revoked if they were found to be routinely breaking the rules of the road, and the carrying of this license conferred some extra benefit to the cyclist, then I would be in favour of that.