Discussed here. Straw man builders, take note. There should probably be a quiz on this stuff at some point.

Oh, I almost forgot. Key passage:

The left is very clever. Defenders of the status quo have created a straw man, and they find quotes from politicians and others with little knowledge to create the impression that advocates of lower tax rates believe in the fiscal version of a perpetual-motion machine. This tactic is then used to prop up the existing system of revenue estimating, which is based on assumptions that would earn an F if put forth by a student in an undergraduate public finance course.