Here's the headline of a Christian Science Monitor story about the killing of Abdullah Abu Azzam, said to be Al Qaeda in Iraq's #2 man: US is logging gains against Al Qaeda in Iraq. But keep reading:

...predicting the real dividends is difficult. "We don't know how many leaders there are, how many experienced cadres there are, how many replacements there are," [Anthony Cordesman of the Center for Strategic and International Studies] says.

Indeed, the US reported killing or capturing at least eight men said to be "top" members of the Zarqawi network in 2004, which did little to degrade the organization's ability to carry out attacks.

It's also not clear what the US defines as a "senior leader," or how hard they are to replace. General Bergner said Friday that since January, US and Iraqi forces have killed or captured at least 80 "senior leaders" in northern Iraq. However, insurgents have been much stronger in the north in 2005 than in 2004.

And it's not even clear whether we've killed Abu Azzam:

...in November 2004, 70 foreign fighters were alleged to have been killed in a single US bombing run on a mosque in Fallujah, which at that time was controlled by insurgents and was under siege by US Marines.

At the time, some news reports said the emir of Anbar Province, an Iraqi called Omar Hadid, was killed in that attack. Some reports also identified him as Abdullah Abu Azzam....

Oh, and throw in this from Reuters:

Abu Musab al-Zarqawi's network of al Qaeda-linked insurgents is emerging as a self-sustaining force, despite repeated blows by U.S. forces and the reported death of his second-in-command, U.S. intelligence officials and other experts say.

The Zarqawi network, responsible for some of the Iraqi insurgency's bloodiest attacks, has grown into a loose confederation of mainly native Iraqis trained by former Baath Party regime officers in explosives, small arms, rockets and surface-to-air missiles....

"He has enough force in place to sustain operations," [one intelligence] official [said]. "Al Qaeda in Iraq ... regenerates very quickly. You knock off a guy who's in charge in a certain area, another person steps into the gap."...

Defense and counterterrorism officials said Zarqawi's insurgents have recently been joined by elements of Jaish Mohammad, a 4,000-member insurgent group loyal to Saddam Hussein's Baathist regime. The addition gives Zaraqwi new tactical skills inside Baghdad, a defense official said.

Although the Jordanian-born Zarqawi has long been associated with foreign fighters, officials believe 85 to 90 percent of al Qaeda in Iraq's members are Iraqi....

Lovely.