Has Bush Made Us Safer?
This article by the Washington Times suggests so. If Khalid Sheik Mohammad (KSM) (one of the top Al Queda operatives before his capture) is telling the truth, the plan was to hit the Sears Tower in Chicago and the Liberty Tower in LA as a follow-up to 9/11. The plan was hindered, according to KSM when the US took out the Afghanistan sanctuary and spent increased effort on disrupting communications.

A few pessimistic points
1) This does not validate the Iraq War as a means to stop terrorism (though future evidence may)
2) This does not address long-term concerns. Losing a sanctuary for the day does not end the danger, especially with increased global anger directed towards the U.S.
3) If we have been so successful at disrupting communication AFTER 9/11, than why didn't we do it beforehand and prevent a terrorist-confidence bonanza and tremendous loss of life and economic dislocation?

A few optimistic points
1) Taking out potential and actual terrorist sanctuaries is a long-term strategy. Afghanistan was used a training ground for thousands of would-be terrorists in schools run by Bin Laden. This will haunt us for years.
2) Further evidence that the Government has been having success against organizations that would do us harm as opposed to Clinton Era appeasement
3) Global anger comes and goes. Showing strength and reasoned patience is what matters in the long run, which is what we are doing now.

(thanks to Angry Clam for the referral)