Strategypage explains how it could be a lot worse:
U.S. government researchers believe the Iran has maintained its tied to al Qaeda, and will seek to increase its influence over al Qaeda in light of the recent death of al Qaeda founder Osama bin Laden. These Iranian al Qaeda connections were initially formed, and subsequently strengthened, by an Iranian organization that specializes in this sort of thing. Bin Laden was not an enthusiastic supporter of the Iranian relationship. But many other al Qaeda leaders were.Yes, Iran has members of al Qaeda "under house arrest." So Iran could emerge as a major supporter of the remnants of al Qaeda to direct this still-potent brand name for Iran's own purposes. We could see Iran provoke more violence in Afghanistan, in Iraq, in Lebanon, in Egypt, and in the Gulf Arab states.
I think we can safely rule out that Iran will give us permission to raid a compound in Iran to kill the next ruler of al Qaeda if he takes up residence within Iran.
Once again, I'd like to note that there is hardly a problem we face in the Middle East that wouldn't be improved by the destruction of the mullah regime in Iran.