Last I checked, Zarqawi was running about 1000 times more operations than Osama. How exactly would HE have been more important to catch at this point in time? You act like Zarqawi and every other terrorist is simply Mohammed Q. Insurgent, and Osama is the only big fish.
What matters right now is:
1) No more American civilians die.
2) No more American soldiers die.
3) The worldwide Terrorist movement does not have any more leaders.
It would be great to have all of them at once, but I'll take 1 & 2 in exchange for 3 any day of the week.