He is, he may be, he isn't dead... Until conclusive proof that he's DEAD is shown to the world then I'll believe he's alive.
I personally think that Bin is blowin in the wind, in bitty little fragments, having long ago taken a direct hit from a very large bomb, and that any eyewitnesses to this event are also blowin, and that you will never see conclusive proof.
Geraldo assured me Osama escaped from Tora Bora. Since then, I have heard W, Cheney, Condi, Rummy and General Myers say the odds are he is still alive (their best guess based on the info). I believe they believe their statements.
I have leaned toward his being dead, but have left room in my thinking for his being alive.