Reposted from a Boing Boing comment
The math and the history makes exact figures difficult, but the idea behind reparations is simple: Because of preferential treatment in the past, one group of people has a position of advantage over another today. Therefore, simply ending the practices that led to the advantage isn't enough.
In pre-Civil War American South, blacks were forced to spend their lives building up the wealth of others, rather than wealth for themselves. After the Civil War, well, same thing.
When the federal government gave away the bulk of the Midwest to homesteaders (and think of the amount of wealth that represents), almost no blacks benefited.
Then, when the government gave millions of WWII vets a free education through the GI Bill, black veterans had a difficult time taking advantage of the gift. The military had been desegregated, but the colleges had not.
So even if we could call ourselves a post-racial society today (we can't), some people would be entering the era of equality as unequals. Poverty is very easy to pass onto one's children, easier than wealth in some ways.
Honestly, I don't believe that formal reparations are the answer. But I think that we as a nation make only token efforts to help poor Americans prosper, or to try to include them in society. If that ever changes, I think the calls for reparations would disappear.