Bush already has provisions for an "October Surprise"--if you listen to shortwave, you find that Bin Laden is already dead and they have him on ice--Rove plans to wheel him out just before the election to ensure a Bush victory. They're not rolling him out now because they know the attention span of the American people is quite limited, and they don't want to waste the spectacular effects of the unveiling this early.
Sad thing is that Bin Laden is only a figurehead, a symbol that AQ rallies around--his presence or absence doesn't stop the daily (and longer-term) operations of the cells, as well as their sympathizers. AQ will continue on without him. An analogy: the death of FDR did not stop the war effort, nor did it stop the march of liberalism in this country.