The ARDrone is completely a toy. It has a range of about 20m before the video cuts out and the quad flies away by itself, crashing into a building or just falling out of the sky.
That said, you can make a long distance plane complete with video, gps and autopilot for $1000 - $2000. Depending on setup, flight time is between 15 minutes and an hour, with effective ranges up to 20km.
HOWEVER, very few people are capable of pulling off long distance FPV. Hell, most people fail at short distance FPV. The gear is hard, radio interference is a huge bitch (especially if you are near any urban area) and frankly, it's hard to fly a little plane made out of foam. They get knocked around by wind gusts really easily.
Any rotor platform (tris, quads, etc) are limited in range to 1-2km max, simply because you can't strap enough batteries onto the thing for longer range. Flight times are 15-30 minutes with current technology
Obviously, technology is going to continue to advance. And if the project is bankrolled by a government, all bets are off. But lone terrorists are going to have a hard time pulling off a drone attack. You can simply triangulate their signal (both the radio control and the video feed, which also usually includes a GPS downlink) and know exactly where they are transmitting from. Interfering with a drone is as simple as jamming the radio spectrum they are using...most drones (planes or quads) have about 10seconds before they crash into the ground when uncontrolled.
Lastly, carrying gear is really hard for any rotor platform. Max payload right now is a couple of kilos, usually a DSLR on a gimbal. These have to be lifted by octocopter setups (8 rotors) which absolutely kills battery efficiency. You get 15 minutes flighttime max, and the thing sounds like a swarm of killer bees.