Airbags smell like gunpowder, are hot and loud, and inflate very quickly because they use a pyrotechnic charge (read: explosives) to inflate.
Mercifully, I have never hit anything other than a parking garage wall dead-on with the gray unpainted plastic of the bumper of my '94 Jeep Grand Cherokee at 1mph, nor have I had anyone else hit me. I've had some close calls, a few of which would've been my fault, many of which would've been other's fault (read: don't tailgate me, and look before changing lanes). I try to learn from each incident, seeing as how I've only been driving for 2 years or so. But, I consider myself lucky, because my insurance group of teenage males has about a 50/50 chance of getting through their first year without an accident.