I would imagine that a UAV would be fairly practical, as has been claimed, in an Afganistan type situation both as a recce vehicle, but subject to the limitations of its sensors, and as a weapons delivery system against fixed targets. Doesn`t matter TOO much if it gets hit by ground launched missiles.I would also imagine that they would be very vulnerable to interception by any manned aircraft that was fast enough to catch it and would be totally useless at intercepting even another UAV let alone a manned aircraft.
Let`s not forget that a Cruise Missile is a UAV.
"Good afternoon Ladies and Gentlemen. Please let me welcome you aboard this, the first passenger flight on a fully automatic aircraft. As you will have noticed, the computers controlling the aircraft have brought us to our cruising altitude of 37,000 feet much more smoothly than any human pilot could have done. Please let me reassure you that this aircraft is perfectly safe as has been proved in many thousands of hours of testing. Every piece of equipment is at least triplicated and absolutely nothing can go wrongongongongongongong.......................
MikeW