Everyone who remembers them has fond memories of the drive-in. By the time I was old enough to enjoy them in the 70's, the peak had passed, and by the 1980's most were gone. There's something wonderful about being in the car with your family as a kid, or girlfriend as a teenager, and taking in a movie at the drive-in.
I remember setting the big speaker on window, checking out the concession stand, and even watching it from the bleachers (or swing-set) when the weather was great. You could take small children and not have to worry about them being perfectly silent, and you could make out with you girlfriend and not worry about the whole theater watching your public display of affection.
Of course, some drive-ins still forbade heavy duty make out sessions. Take a look at these actual frames from a warning issued by the drive-in management:
I doubt many teenagers took this warning to heart; in fact, I'm sure it inspired a fair share of laughter. You've got to give them points for trying, though.
One of my wife's fondest memories is being loaded up with her siblings into the station wagon with blankets and pillows and heading to the drive-in. It was generally not a great movie (often intended for adults), but it was the experience not the film itself that made it memorable years later. I'd love to do the same with my kids, but, sadly, there's no drive-ins nearby.
If you'll recall, drive-ins used to show a lot of low budget stuff which cost very little. Movies like Swedish Fly Girls and Billy Jack don't attact crowds like they used. to.