I've never had a problem with scissor jacks breaking, but I did have one little mishap but it was my fault. I almost had the front end of an early 90's plymouth come down on my chest because I was dumb enough to use a scissor jack when the car was on a bit of a slope.

 

I've done that too. Drive up on a couple of 2 x 4's and then slip a floor jack under. Gets the job done nicely, actually.