There's no news hook to this post, except for the fact that maybe sanctions will someday be levied against Iran and Syria. Or threatened to be levied. Or whatever. Still, sanctions are going to make some sort of appearance on the world stage, so I googled around and found this 1998 article by Dan Drezner, "Serious About Sanctions," that lays out the real dirt on sanctions. The main points, in bullet form (with some commentary in parentheses):

Sanctions do work, sometimes. A study of 116 "sanctions episodes" between 1914 and 1990 concluded that they succeeded a third of the time, failed a third of the time, and partially succeeded a third of the time.

Sanctions tend to work better against allies than adversaries, since adversaries prefer near-term economic costs to longer term political ones. (Which, of course, explains Iran's current behavior—the question is whether near-term economic costs resulting from sanctions will be so crippling as to be worth giving up a major strategic asset, i.e. nukes.)

There's no correlation between the effectiveness of sanctions and whether the targeted regime is democratic.

Multilateral sanctions are much more effective if done through an existing organization like the UN, since targeted regimes have less reason to think that there will be defections anytime soon. (Saddam Hussein, of course, undermined UN sanctions, but he had to go to spectacular lengths and even then, just didn't get very far. If anything, his example might make UN sanctions more credible in the future.)

Unilateral sanctions can work, since it's not always obvious that the sanctioned country can just find other countries to trade with. Especially nowadays, with the Soviet Union gone, restricting U.S. aid can be a powerful lever, as can freezing financial assets.

Most sanctions don't hurt U.S. firms, since they either don't impinge on bilateral trade (targeting aid instead) and besides, the U.S. can shift to other markets.

Sanctions can increase the chance of war. Obviously they can provoke war, as was the case with Japan in 1941, but they can also be prone to "mission creep." The U.S. may be pushed into more severe action when sanctions don't have the desired effect.

Sanctions often have unintended consequences—creating black markets, for instance.

Obvious point, but "sanctions that serve particular interests are just another form of protectionism." Also, the wonky point that Congressional mandates for sanctions have all sorts of ill-effects and aren't as threatening as thought. Read the article for that.

Good stuff to know. And really interesting article.