Do read Piketty's Garden of Envy, Theodore Dalrymple's review of a book he hasn't yet read. An excerpt here:
"As to the tax on capital, Piketty is right to say that it must be global, for otherwise there would be capital flight or very severe local restrictions on capital movement, neither of which would be economically productive or conducive to equality. A global tax on capital, however, would require a global authority to raise, collect, and enforce it, a kind of giant European Union in fact. I am glad I shall not live to see it, but I doubt that anyone else will live to see it either, born or unborn, if only because the governors in the world government would need a tax haven in which to put their own money."