I agree w/ jrhc on this.
I think that it would make the system fairer. If everyone is paying for products that they use, it would be pretty hard for wealthy corporations and individuals to get out of paying it since it's pretty straight forward- buy the product, pay a tax, don't buy the product and pay no tax.
However, I think that politically it is not feasible. People will be skeptical about the tax rates for individual sales. For instance, what if buying stock is being tax at 8%, while buying a car for the price of $500-%10,000 is taxed at 13$? It'll appear as if the products that the rich purchase are taxed less heavily, whereas the products that the poor/middle class buy at taxed more heavily. In turn, we've done nothing but waste thousands reforming the system and continue w/ the same old political system of favoring a certain group. Also, you have to keep in mind that the powerful lobbyist group and political doners, known as lawyers, will certainly oppose this. Tax lawyers are some of the best paid lawyers b/c they benefit from the complexity of the current tax system. They, of course, will be the ones that will lose if the current system is reformed since there will be little need for them.
I think a flat tax is much more feasible and fairer than a VAT. In Russia, they have a flat tax set at 13%. It has attracted a lot of investment into Moscow. Overall, I think it is administered pretty fairly. However, hardly anyone in Russia pays their taxes, but that is more of an administrative problem. Although a problem like that is much less common in the US, you will always need a bureaucracy to make sure that everyone is paying their taxes.