No, not porn. Organs. From Dubner & Levitt (of Freakonomics fame) comes Flesh Trade:

Alvin Roth, even though he is an economist, is smart enough to realize that repugnance will keep Americans from embracing a true market for organs anytime soon. So, along with several other scholars and medical personnel, he has helped design a clever alternative, the New England Program for Kidney Exchange. Imagine that you have a wife who is dying of renal failure, and that you would give her one of your kidneys, but you are not a biological match. Now imagine that another couple is in the same bind. The kidney exchange locates and matches the couples: you donate your kidney to the stranger’s wife, while the stranger gives his kidney to your wife; the operations are performed simultaneously to make sure no one backs out. Although this system has yielded only a couple dozen transplants so far, it illustrates an economist’s understanding of incentives: if you can’t get someone to give an organ out of altruism, and you can’t pay him either, what do you do? Find two parties who are desperate to align their incentives.

Brilliant. Another case of the long tail. Finding two parties with this kind of aligned incentives by buying an ad in the local newspaper? Impossible. Finding them on the internet? Very doable.

Brilliant.