Al Qaeda does have a strategy for this phase of its war with the US. It’s called “superpower baiting.” This strategy works on the simple premise that the US over responds to humiliation.
Our over response to humiliating attacks usually takes the form of conventional military force: invasions, bombings, sieges, and search/destroy missions. These conventional attacks are easy and provide immediate gratification, however, everytime we do respond in this manner, the US becomes more isolated.
Isolated from our allies and each other. Isolated from our real objectives based on the facts available to us. Isolated from our morals and codes of conduct. In the end, when we are fully isolated, we become Israel.
If this is al Qaeda’s strategy — to goad the US to transform itself into Israel — then the beheading of Nick Berg makes sense. This act of humiliation serves to steel our resolve to stay in Iraq, in the wake of the Abu Ghraib debacle. It keeps us in place to continue the process of isolation.