Zarqawi's death

U.S. military is basically persuing the bottom and working to the top. Each time they nab a guy like this they get more intel. So maybe with getting more intel they will be able to find Osama Bin Laden.

Another thing is sure they have someone in place. But you take enough of the top leadership out, it will have an impact on the Al quita's ability to organize. Also, it will send a message to discourage people from joining in the first place.