The current proclamation gives to much power to Bush, it essentially gives him the authority to attack anybody he wants in any way he wants. Remember that Bush doesn't need congress to allow him to make use of the military, he only needs congress if he actually wants to run a war.
An actual declaration of war would be even worse. Imagine what would happen if we did that and it turned out that bin Ladin was taking money from renegade British nobles who hated the US for overthrowing British rule those many years ago. Oops, we just accidently declared war on our closest ally.
Heck, what if bin Ladin is taking money from radicals in the US. Then we accidently declared war on ourselves. Though it would be profoundly amusing at a moral level, it would be an international disaster.
Jay