We use autopilot a lot. It depends on the size of the airplane primarily as to how much we use it, but on long haul international flights it is probably closer to 98...99%. After about 2-3000 feet and then on approach down to about 2000 feet. We can do autolands on pretty much any airliner that exists today. The takeoff part of the equation is the one that is probably hardest to solve, but pigboy did talk about predators etc... I think the issue with that right now is mostly reliability of signal. You need 100% reliability. And then there's security. I can see one pilot on board for takeoff/landing then he gets into his jammies unless needed or until descent. However.... see Germanwings....
The cruise part could absolutely be autonomous. Takeoff/climb... descent/approach/landing are not quite there yet, but it is getting closer everyday. You'll never see me get on one however.
Oh.. and I think while trucks only have 2 dimensions, they have to be able dodge something closing at 120 mph in a split second if it looks like it is gonna get hit head on. Airplanes are in a very very controlled environment for the majority of their mission. If we get within 500 feet of something in flight, everybody freaks out. Trucks miss each other by 6 feet all day long.