The effectiveness of drone strikes
NPR story here.
Link to full paper here.
I'd say it's effective enough on the terrorists they hit, and I can't think of any better way of attacking a widely-distributed enemy with minimal losses. Sure as hell beats carpet bombing from B-52s, and given current technology the only other things that could do the same thing better would be invisible ninjas or teleporting snipers.
I supported this kind of operation when Bush started doing it, and I still support it.