On this issue, Barack Obama has normally taken a hardline stance. His boldest statement came during this speech.
"I understand that President Musharraf has his own challenges," Obama said, "but let me make this clear. There are terrorists holed up in those mountains who murdered 3,000 Americans. They are plotting to strike again. It was a terrible mistake to fail to act when we had a chance to take out an al Qaeda leadership meeting in 2005. If we have actionable intelligence about high-value terrorist targets and President Musharraf won't act, we will."
Now, with a complex issue like the GWOT, it is easy to be a critic. What is more difficult is actually having to execute a policy for the GWOT. Obama has criticized everything from our invasion of Iraq, Afghanistan, warrantless wiretaps, torture, GITMO, and not catching UBL. That's because no matter what Bush does there will always be room for criticism. If he is aggressive you can go after him on civil rights issues. If he isn't then you can criticize him for not being aggressive enough. No matter the policy there is always room for criticism.
The reality of the hunt for UBL is a lot more complicated than fiery rhetoric of Barack Obama. The reality is that an airstrike would take an enormous amount of luck. It could happen but we would have to be lucky. In order to make a full effort to take out UBL, we would need to make a ground attack. We would have to disperse troops have them go village to village and gain enough intelligence until UBL was simply cornered.
The problem is that Pakistan has maitained its sovereign rights over its nation and refuses to allow U.S. ground forces into its nation. If we sent in ground forces over their objections, it would be an act of war. On a practical level, it would likely either cause a confrontation with the government or simply topple it. Now, Pakistan is no perfect ally, but given that it is sitting on nuclear weapons, we could do significantly worse than the current government.
In fact, it is quite likely that if the government fell, it could likely be replaced by an Islamist government. That government would now have access to nuclear weapons.
If we sent in ground troops, that means a full scale war. If the government fell because the people rose up in defiance, a likely scenario if the government doesn't confront our military, then killing UBL would only be the beginning of the operation. We would have to then rebuild yet another nation. Now, if you think that either Iraq or Afghanistan have been difficult you have no idea what Pakistan would be like.
Or, there is the other scenario. The government confronts us and we turn an ally into an enemy.
Either scenario is not very appealing. Everyone wants to bring UBL to justice however there are geopolitical realities that Obama simply disregards in order to make a political point. Or even worse, he simply doesn't understand them enough and attacks anyway. Either way, catching UBL is not as simple as the fiery Obama rhetoric makes it out to be.