I predict that Bin Ladin or Zawahiri, or both, will be captured or killed within the next 6 months. Why? The general who ramped up the efforts to kill Zarqawi is on the hunt: Lt. Gen. Stanley A. McCrystal. My past posts "Task Force 145's Greatest Hits" and "the Big Hit" detail the extraordinarily aggressive raids by Gen. McChrystal's forces that led to the killing of Zarqawi in Iraq. This (This link is now dead. I think the article ran in the Washington Post. Another article on the subject is here) MSNBC report reveals this excellent development and further reveals that for High Value Targets, like Zawahiri and Bin Ladin, McChrystal's forces may strike in Pakistan. Both HVTs are believed to be in the tribal areas of Pakistan.
Update: It is 2/13/07 and I am going to preemptively call myself wrong on this one. Given the peace agreements signed by the Pakistani government with the Taliban in the tribal areas of Pakistan and the complete collapse of of the Bush administration's will to fight the war on militant Islam, there is no chance that this prediction will come true.