Econo-Girl feels the need to expand on her earlier analysis. Al Qaida had the idea that the cause of their brand of Islam could be advanced better if other Muslims weren't at their throats. A good idea, if hardly original.
So that's how they started out. If Sunni and Shiite were not exactly co-recruiting, then at least they weren't killing each other. The new dynamic allowed Al Qaida to focus on attacking the West.
Then came Iraq. To take on the U.S. in Iraq, Al Qaida started fighting between the Shiite and the Sunni by attacking the Sunni. Yes, that has hurt U.S. success in rebuilding Iraq. But it has eliminated Al Qaida as a global political force.
By attacking Shiites in Iraq through Zarqawi, Al Qaida has opened the door to sectarian attacks on themselves. Their ostensible goal of an Islamic caliphate in the Middle East is gone.
Econo-Girl has said it before, and she means it. There will be high level assassinations within the radical Islamic community. Maybe not immediately, but it is coming.