Micah Zenko at the Council on Foreign Relations website:
Pir Zubair Shah: My answer is that in Pakistan, targeted killings have worked to a large extent—CIA operated drone strikes have eliminated top al-Qaeda and local Taliban leadership. The tribal region of Pakistan along the Afghanistan border turned into a safe haven for the Taliban and other foreign fighters affiliated with groups like al-Qaeda and the Islamic Movement of Uzbekistan (IMU) that fled Afghanistan in the wake of the U.S. invasion. Because Pakistan was unable and sometimes unwilling to take on such groups, drone strikes became the only politically viable option for U.S. counterterrorism goals, such as destroying al-Qaeda safe heavens.
The first known case of targeted killing by a drone strike is when a Pakistani Taliban commander, Nek Mohammad, was killed in 2004. Since then, more than three hundred strikes have killed dozens of al-Qaeda leaders and local insurgent commanders. The main focus of the drone attacks have been the tribal districts of South and North Waziristan, where al-Qaeda militants and other foreign fighters took refuge after the fall of the Taliban regime in Afghanistan. Drone strikes have also killed fighters who posed a greater threat to Pakistan than to the United States, including commanders like Baitullah Mehsud, Qari Hussain, and Badar Mansoor. Similarly, some of the top al-Qaeda commanders were Abu Yahya al Libi, Khalid Habib, Osama Alkini, and many others. Drones have also killed the head of IMU, Qari Tahir Yeldeshev, and the commander of the Eastern Turkistan Movement in North Waziristan. In recent months, drones have also targeted members of the Haqqani network, including the sons of Jalaluddin Haqqani, the symbolic head of the network that is now run by his son from safe havens in North Waziristan and other places in Pakistan.
Drone strikes have also resulted in civilian deaths, although far less than what is reported (mostly) in Pakistani media. The number of civilians killed by drones is also fewer than those killed by Pakistani jet bombers and artillery shelling. Similarly, the tribal areas targeted by drones have a favorable view of the attacks, compared to mainstream Pakistani society, who view the strikes as violations of their national sovereignty.