Now that al=Zarkawi is dead, it's clear that the attack on his safe house was even more of a success than previously noted. Evidently the "emir" kept copious records with him. This really isn't all that surprising--a year ago al-Zarkawi was nearly captured by coalition forces, escaping while carrying little more than his notebook computer. His files were as valuable as his life then, and they are more valuable today.
So what's in there? Names, locations, sources of funding, sources of intelligence, plans, communications with other organizations...we can only speculate. And there's no way we'll find out, I hope, until well after the last of the infornation is exploited. Today every member of the al-Zarqawi network, every ally, every client, every informer, every supplier has to assume the worst: that everything has been compromised. There are a lot of people looking for new places of safety today.
Moreover, consider what the ability to target that house means for coalition intelligence. Assuming any reasonable operational security for Al-Zarkawi and company, and the fact that house was well away from others, it can't help but make you wonder if the key source was a ranking (or at least middle-rank) member of the network. Even if that isn't the case, any reasonable (?) terrorist has to assume that he can't trust the people he works with. That, in turn, leads to delays, mistakes, and even new informers (who want to get the best deal they can from the coalition, while they still have the chance).
Let's not go overboard here: al-Zarqawi wasn't Al-Qaida in Iraq, and Al-Qaida in Iraq is not the sum (or even the majority) of the insurgency. But it is a major victory, a victory that goes well beyond the death of a homicidal thug.