Well, everybody, there has been some discussion of this topic, but I wanted to get more feedback.

I learned from my father to use a heavy cinder block and wood to support the car when doing under-car work. This was before the days of jackstands.

Someone wrote that somebody was killed using a cinder block support. My reply to that was that he had probably oriented the cinder block the wrong way. The cinder block should be oriented so that the holes are vertical, as that is where all the compression strength comes from. After all, they don't construct buildings with the holes facing sideways. Someone wrote back that the cinder block strength comes from being tied together as a unit with other blocks and from the rebar and concrete fill. While this is true, this adds tensile strength (twisting and pulling lengthwise). My argument is that the compression strength of a single block is enough to hold the weight of the car. Could I be wrong?

Actually, for further safety, my technique is to use a cinder block (and wood) and one jackstand for each side. The reason I don't trust jackstands alone is that I had once incompletely inserted the tab into the lock jaw and, while I was working underneath the car, the other side started to slowly lower itself. Needless to say, I got the hell out from under the car real quickly.

Another technique is to back up the jackstand with the floorjack.

Any comments?