For one, my team and I were often referred to as crusaders by Iraqis that didn't realize the 6'4 blond guy next to me spoke perfect Arabic. I've also had some research time on the counterterrorism issue, and you'd be suprised how often the concept of the Crusades comes up. It's at least as common as we mention the Islamic concept of jihad, and probably more so. Bin Laden uses the term in practically every speech he's ever given, and it's widely used in mosques and madrassas as a way of referring to westerners.
That's just off the top of my head, though. I don't have any links handy.
In that sense, "avenge the Crusades" for Muslims in the Middle East is probably no different than "George Bush destroyed the levees in New Orleans" among Americans like Louis Farrakhan.
I think those are sufficient examples to prove your point. I definitely recall Bin Laden using such references.
Nonetheless, I do think that it is a more contemporary training in how to break down the Western system. How can we guilt the West into giving itself up? They know we feel guilty for the crusades.
I tend to agree with other posters that the Crusades were a response to imperial aggression of the Islamic world. Seizure of Jerusalem was an emphatic point of domination. Further seizures in Europe also demonstrated their aggressive practice.
Our responses continue to be rather tame.
I'd consider it likely that the Crusades references were added on after the fact as a means to marshal the troops.
(Ending slavery came after maintaining the union. Saving European Jewry came after stopping Germany expansionism. I'm pretty confident that stopping Serbian ethnic cleansing came after some very Machiavellian decisions were made in Berlin.)
PS: The few Muslims I know are hard over on US-Israeli linkage and stone silent on the Crusades.