Yes, the ongoing involvement of the United States armed forces in Afghanistan is effective at thwarting Al Qaida, because we have taken out many of the highest leaders. Terrorist attacked today are either headed by other organizations, like the Boston Bombings, or they are done by regional groups, like the terrorism in Kenya.
It is my opinion that the armed forces of the United States are effective at combating the various actions and threats posed by the extremist group known as Al Qaida in Afghanistan. I feel that Al Qaida would be much more difficult to oppose if American troops were not present in Afghanistan.
Yes, the ongoing involvement of the United States armed forces in Afghanistan is effective at thwarting Al Qaida. The U.S. military is able to stop, or attempt to strop, terrorism at one of its key sources. In addition to terrorism 'born' in Afghanistan the country has always been a refuge for terrorists from beyond its borders. There is no telling how much terrorism has been stopped thanks the United States armed forces.
Al-Qaeda is hardly worth the United States time in dealing with, and is likely just an excuse for other reasons to be in the Middle East. If we think really hard about it, we can see that the Middle East has the worlds largest supply of oil, which is the real reason we are "thwarting" Al-Qaeda.