For what it's worth, I have heard a number of 9-11 jokes -- none that I would repeat, mind you. One of the things that you do have to keep in mind, though, is that in much of the world outside the US, the United States' prosecution of the war has led to a kind of backlash. There are people who, while not necessarily advocates of the kind of violence visited on American on September 11, who have had their sympathy for America sapped. This is how they express their frustration.