Now that you mention it - a few years ago I was involved in a fairly serious car crash, rammed from behind by another vehicle at high speed. I suffered a minor neck injury, sprained shoulder and some bruising. I was able to deploy my folding knife clipped to my front cargo pocket without any difficulty. It was completely instinctive on my part, I did it without really thinking about it. Just as I was about to cut the seatbelt though I figured I ought to give the buckle another try and managed to disengage it just fine. So no cutting was required that day.

You're absolutely right that specialized heavy duty tools are much more effective for rescue applications, but unfortunately they're seldom available when needed. A simpler tool such as a large screwdriver, fixed blade knife etc. can come in handy in that kind of situation if no better alternative is at hand. Not necessarily the most professional or efficient way to do it, but it just might work. I have (ab)used the Glock knife for a similar application with some success in a couple of occasions - thankfully never in a real life or death situation. I also used an entreching tool once to pry open a jammed door. It wasn't pretty but it did the trick luckily. The Gerber LMF II has been quite popular in some branches of the military lately for the same purpose. I'm sure a proper crowbar or rescue tool would work much better still if you can get hold of one in time.