The either-or nature of the question misses the point. The reality is that we face BOTH a decentralized Al Qaeda manifested by self-radicalized or homegrown "bunches of guys" for whom the al Qaeda name is just a brand or symbol AND a centralized, core al Qaeda group which is still plotting and planning attacks from the Afghan/Pakistan frontier.

As I noted earlier in this discussion thread, the threat today comes from al Qaeda core, al Qaeda affiliates, and local cells. There is much to be said of both Sageman and Hoffman's analyses, but the assumption that the core al Qaeda threat is behind us is simply belied by everything we hear from the intelligence and law enforcement communities. Recognizing the evolution toward a core group that functions as a type of symbolic leadership for a broad and decentralized movement is equally important. To date there is still no clear link between the Madrid bombers and the al Qaeda core. The link between al Qaeda and the London bombers, however, is pretty clear.

But it is also true that part of the successful evolutionary change within al Qaeda has been due to its resilience. Each time we take out an al Qaeda military commnander (Khalid Sheik Mohammed, al-Libbi, Hamza al-Ribai...) another comes along. These terrorist tacticians, however, are far more important today than Bin Laden himself. Even within the al Qaeda core leadership, it is Ayman al-Zawahiri who is the brains behind the group, as is especially evident looking at the group's media and propaganda efforts. Capturing or killing Bin Laden would be a major psychological blow to al Qaeda (and perhaps more so to the local and independent but like-minded fellow travelers), and it would be a significant accomplishment and morale booster for the Western coalition, but it would do nothing to actually harm, diminish the capabilities of or undercut support for al Qaeda. Al Qaeda today has outgrown Bin Laden.