The Iraqis are pissed, and they aren't going to take it anymore. They recognize the hand of the foreigners that have brought them suffering and humiliation. These guys are angry and they are taking the fight to the enemy: Abu Musab al-Zarqawi.
If nothing else, this at least shows that some Iraqis are picking up on the American way of "If no one else is going to get it done, then I will." At least I still think that is an American way.
Disclaimer for those who lack a sense of judgement: I am not advocating vigilantism in the United States. I am just very glad to see that there are people in Iraq who do not immediately blame the US as the sole responsibility holder for all of the bad things that happen in their world.