I guess we should give the New Monetarists a chance to weigh in on Milton Friedman's legacy and influence (their name -- New Monetarists -- should give you some idea where this is headed...I cut the specific arguments short, but they can be found at the original post):
Friedman's Legacy, by Stephen Williamson, New Monetarist Economics: I'm not sure why, but there has been a lot of blogosphere writing on Milton Friedman recently... Randy Wright once convinced me that we should call ourselves New Monetarists, and we wrote a couple of papers (this one, and this one) in which we try to get a grip on what that means. As New Monetarists, we think we have something to say about Friedman.
We can find plenty of faults in Friedman's ideas, but those ideas - reflected in Friedman's theoretical and empirical work - are deeply embedded in much of what we do as economists in the 21st century. By modern standards, Friedman was a crude economic theorist, but he used the simple tools he had available to develop deep ideas that were later fleshed out in fully-articulated economic models. His empirical work was highly influential and serves as a key reference point for some sub-fields in economics. Some examples:
1. Permanent Income Theory...
2. The Friedman rule: Don't confuse this with the constant money growth rule, which comes from "The Role for Monetary Policy." The "Friedman rule" is the policy rule in the "Optimum Quantity of Money" essay. Basically, the nominal interest rate reflects a distortion. Eliminating that distortion requires reducing the nominal interest rate to zero in all states of the world, and that's what monetary policy should be aimed at doing... We can think of plenty of good reasons why optimal monetary policy could take us away from the Friedman rule in practice, but whenever someone makes an argument for some monetary policy rule, we have to first ask the question: why isn't that rule the Friedman rule? The Friedman rule is fundamental in monetary theory.
3. Monetary history: Friedman and Schwartz's "Monetary History of the United States" was monumental. ...
4. Policy rules: The rule that Friedman wanted central banks to follow was not the Friedman rule, but a constant-money-growth rule... Friedman was successful in getting the rule adopted by central banks in the 1970s and 1980s, but the rule was a practical failure, for reasons that are well-understood. But Friedman got macroeconomists and policymakers thinking about policy rules and how they work. Out of that thinking came ideas about central bank commitment, Taylor rules, inflation targeting, nominal GDP targeting, thresholds, etc., that form the basis for modern analysis of central bank policy.
5. Money and Inflation: ... Friedman played a key role in convincing economists and policymakers that central banks could, and should, control inflation. That seems as natural today as saying that rain falls from the sky, and that's part of Friedman's influence.
6. Narrow banking: I tend to think this was one of Friedman's bad ideas, but it's been very influential. Friedman advocated a 100% reserve requirement in "A Program for Monetary Stability." ...
6. Counterpoint to Keynesian economics: Some people seem to think that Friedman was actually a Keynesian at heart, but he sure got on Tobin's nerves. Criticism is important - it helps to prevent and root out lazy science. Old Keynesian economics was probably much better - e.g. there would have been no "neoclassical synthesis" - because of Friedman.
If anyone wants to argue that Friedman is now unimportant for modern economics, that's like saying Bob Dylan is unimportant for modern music. Today, Bob Dylan is quite willing to climb on a stage and perform with a world-class group of musicians - but it's truly pathetic. Nevertheless, Bob Dylan doesn't get booed off the stage today, because people recognize his importance. In the 1960s, he got people riled up, everyone paid attention, and the world is much different today than it would have been if he had not done the work he did.