For one thing, I do not see the reason why the entire *United States* should carry the burden of such reparations. Not the whole country institued slavery, only several states. In fact, the United States fought a war against those states and abolished slavery. So it is the states that actually had slavery should be responsible for the reparations - a progressive reparation tax (e.g. starting from a $75 k threshold - on the assumption that it was mostly the rich who benefited from slavery) imposed on the Dixie states would not be such a bad idea after all - especially if the money was used to fund institutions charged with undoing effects of slavery, such as education or job training, rather than individual payments.
wojtek