Over at The Volokh Conspiracy, David Kopel does a great job of defining Godwin's Law, including these subsets:

In what situations are modern-day comparisons to the Nazis likely to follow Godwin’s Policy of being useful, rather than trivial or hyperbolic? There are several obvious cases for which the Nazi comparison is neither hyperbolic nor trivial, even though the case in question may have some significant differences from the Nazis. This list is meant to be suggestive, not comprehensive:

1. When discussing followers and leaders of a political movement that is explicitly founded on Nazi principles or my admirers/allies of Nazism. These would include some, but not all, of the racist hate groups. These also include the Ba’ath parties of Iraq and Syria, since Ba’ath was founded as an Arab nationalist syncretic blend of Nazism and Stalinism.

2. When discussing somebody who adopts the nickname “Hitler,” as well as followers and cohorts of such a person. This would include Zimbabwe, where the late right-hand man of the tyrant Robert Mugabe was Chenjerai "Hitler" Hunzvi. It also includes the Fatah Party in the Palestinian Authority, one of whose members of the national assembly, Jamal Abu Roub, sports the nickname "Hitler."

Regarding that last item, Jonah Goldberg writes:

In 1996, Daniel Jonah Goldhagen wrote a hugely controversial book, Hitler's Willing Executioners. The thesis was straightforward: The German people were in on the Holocaust; German culture and history harbored and nurtured an "exterminationist" version of anti-Semitism that simply awaited ignition from Nazism's torch.

Goldhagen's thesis was overstated but fundamentally accurate. There was something unique to Germany that made its fascism genocidal. Around the globe there have been dozens of self-declared fascist movements (and a good deal more that go by different labels), and few of them have embraced Nazi-style genocide. Indeed, fascist Spain was a haven for Jews during the Holocaust.

Goldhagen's book was immensely controversial in Germany, where an odd cult of victimhood had settled in. According to the victimhood view, Germany was in effect "occupied" by the Nazis, and the German people were victims, too. Obviously, this is a very convenient interpretation for a country understandably desperate to distance itself from the Holocaust and various brutal military adventures.

But variations of the don't-blame-the-people thesis have been around for a long time far outside of Germany. Democracy can be wonderful, but some of its boosters across the ideological spectrum assume that all democratic outcomes are good outcomes, and that's nonsense. The Left historically has located political morality in the interests and desires of the masses, therefore pronouncing it heretical to blame "the people" for evil deeds. In order to be evil, it seems, causes must be "hijacked" by small cabals of bad guys.

The classic Marxist definition of fascism, put forward in 1935 by Georgi Dimitroff, holds that fascism is "the open terroristic dictatorship of the most reactionary, most chauvinistic and most imperialist elements of finance capital." This notion that the Nazis were the fighting brigade of the rich and powerful has had a remarkable shelf life. The only problem, as countless scholars have demonstrated over the years, is that this isn't true. Nazism was a popular movement that crossed all class and regional lines in Germany. Hitler was hardly a tool of the rich, and to the extent he was helped by a few wealthy individuals, the fact remains that the Nazis achieved their electoral success by portraying themselves as defenders of the little guy and of national pride.

Today, various pragmatists, optimists, and apologists for the Palestinians say they weren't voting for mass murder and terror, but for honest government and efficient social services. Fatah, the "party" of that terrorist carbuncle Yasser Arafat, was corrupt and incompetent while Hamas has successfully delivered much-needed social services. Hamas ran on "change and reform," proclaim the apologists, not terrorism. Fine, but that was equally true of the Nazis, who traded soup kitchens for indoctrination. Fascist movements have always gained popularity by delivering for the needy, the forgotten, and the left-out. They have always captured the imagination of the middle class by promising to reform the government, root out corruption, make the trains run on time. And fascist movements have always promised, as Hamas has, to bring about a moral and national restoration.

The overnight nostalgia for Fatah is, of course, laughable. It hardly governed as a party of peace, democracy, and secularism. But looked at through the eyes of many Palestinians, it probably looked a lot like the Weimar government did to many Germans: institutionally corrupt, ineffective, and tainted by humiliating concessions to foreign powers and occupiers. (People forget how much the League of Nations carved up Germany — and how much it rankled Germans).

There are serious differences between German or Italian fascism and Hamas's Islamism. But these are largely intellectual and academic distinctions. As a social phenomenon, the Palestinians voted for politicians such as Mrs. Farahat. She belongs to a brutal, terroristic, irredentist, militant organization dedicated to restoring national pride at the expense of exterminating millions of people, who just happen to be Jews. This was no secret, and it is a form of condescension bordering on infantilism to assert that the Palestinians didn't know what they were voting for. If the new government had the means, it would be Palestine's willing executioners.