It is important to recognize the power bin Laden has as a symbol. His success in attacking America, and subsequent survival, acts as an inspiration to jihadis around the world. al-Qaeda has become a brand, with franchises around the world. Osama doesn't have direct control of these groups, nor does he need to. His words have achieved the goal of motivating a number of small terrorist groups around the world. Notice the number of groups arrested in Europe.
Which brings me to the point of how best to combat terrorism. This is not a military conflict, and won't be defeated by invading countries. Instead, it is an intelligence conflict. Notice that the majority of terrorist plots that have been foiled were as a result of informants.
There are 2 tactics which can effectively stop terrorist attacks.
1. Infiltrate. Old fashioned spy work. Not easy to do, and very risky for the spies, but quite effective. As an example, let's remember John Walker Lindh. The kid from Marin County joined the Taliban, and met bin Laden several times. While it appears that he was sincere when he joined, just the fact that he was able to get "inside" shows that there is an opening for planting someone within al-Qaeda. If al-Qaeda and like minded groups become riddled with spies, they will become paralyzed as plots are foiled and picked off one by one.
2. Better coordination with foreign intelligence. With so many countries in the world facing the threat of terrorist attacks, there's a lot of motivation to share more intelligence. While it means working with some unsavory regimes, there are mutual benefits. An example would be Syria. The Assad government is almost as hated by al-Qaeda as the American government, and if treated diplomatically would be a valuable ally. Our current administration's policy of confrontation instead of engagement makes us more vulnerable to terrorists, and needs to be reversed.
We do need to kill or capture Osama bin Laden for symbolic reasons. His continued ability to motivate attacks after six years makes us look like a paper tiger. Removing Osama won't stop terrorism, but it will be a psychological victory. The fact that he's still present, and able to taunt America, is a sign of how incompetent our shrub is.