I suppose it sort of works like the autopilot in a plane, except that the autopilot in a plane is usually connected to most of the control surfaces on the plane in addition to throttle, while cruise control on a car is only connected to the throttle (and brakes in some very modern cars). The tech is developing, though. A few cars on the market can already park themselves, and of course Google's working on fully autonomous cars.
Well, since in a modern car, the steering "defaults" to going straight, so in essence, it works like an airplane autopilot. Even in a Viper, it'll just keep you going straight and level, control surfaces link is just so that it can set trims. Super Hornet has a more advanced autopilot (it can fly steerpoints and even land itself on a carrier, though not on a runway, oddly), but it's a latest-generation naval fighter. Latest airliner and business jet models probably also have this kind of autopilot, but in the vast majority of planes, holding course/altitude (or both at the same time) is everything it can do.
Perhaps we'll get an automatic car someday, but I'm skeptical. The computers usually are the first thing to break down. As long as it causes it to show a stupid fuel consumption figure (due to the car running on LPG, which usually drives the performance adjuster crazy), there's no problem. If it causes the computer-controlled brakes to stop working while cruising on a highway, well, that's a bit worse. Also, GPS navigation often has accuracy problems. For example, on the German-Polish border there's a river. Once upon a time, there was a bridge on it, near the border crossing. The thing is, there isn't now, replaced by a guy with a dinghy. Well, huge trucks used to line up in there, because GPS insisted the bridge (gone since 20 or so years!) still stands. If the thing was actually driving, it'd probably drive straight into the river. I'd rather rely on my own common sense, leaving GPS to plot a rough course and show a map.
