Incentives for Marrow Donors
The Institute for Justice has filed suit to overturn the federal prohibition on financially compensating bone-marrow donors. Megan McArdle has a good post on the subject.
I do take issue with the idea that bone marrow should be exempt from the federal prohibition because, like blood or sperm (but not eggs), it regenerates. The same is functionally true of kidneys, where the remaining organ grows to take up the slack; liver lobes also regenerate.