Wired has been really good the last two months, after a couple of sleepers. They have an article this month about NetJets (warning: Flash intro, but tasteful), 'the leader in fractional aircraft ownership.' The founder, Richard Santulli, is a mathematician.

The problem: if he sold a certain number of shared planes to customers, how many extra planes would he have to own in order to cover all the overlaps in customer demand?

The answer: 5.25 extra planes for every 20 planes owned. Now he has a 1 billion$+ company which Warren Buffet recently bought. Amazing.