Over at NRO, Duncan Currie gives it his best shot:
Despite being more efficient than an ordinary sales tax, a VAT carries significant administrative costs, and piling it on top of the present U.S. tax structure would be a mistake. But using the VAT to eliminate a sizable amount of distortionary U.S. income taxes would yield a far more growth-friendly system than the one we have today. Over the long run, America must reorient its economy away from consumption and toward investment while boosting its dangerously low savings rate. A VAT is certainly not the only way to promote those objectives, but it should at least be part of the conversation.
This is the kind of thing that really burns me. Here is Simon Johnson, former chief economist at the IMF, over the at the NYTimes econ blog: