Business Week's Chief Economist Michael Mandel has the best short, accessible description I have seen of the raging debate among "salt water" and "fresh water" economists over the stimulus. For the anti-stimulus crowd, he might have added the argument that a stimulus will delay the painful collapse and cleansing needed to renew sustained growth. (This is an Austrian, not really Chicago, point of view. But it's an important point in the overall debate.) Otherwise a great summary. The whole thing is worth reading.

... we are getting the equivalent of a full-scale intellectual war, with Nobel prize winners and leading economists actively attacking each other in public... It's important to understand that the vehemence of this debate reflects the resumption of an intellectual conflict that dates to the Great Depression and the famous economist John Maynard Keynes. The question then was whether the New Deal helped shorten or soften the Depression, as Keynes argued, or whether government intervention actually hurt the economy.

Surprisingly, the evidence is ambiguous...

In the end, this near-depression is likely to be a transformative event for macroeconomics. We are going to have a mammoth fiscal stimulus package this year—and in all likelihood, more in the near future. And when we see what happens, we may finally settle some of the disputes that have bedeviled economics for 80 years.