As with most toys today unfortunately they aren't made like the old metal Tonka trucks that today, I would feel safer sitting on and rolling down my hill in than my Hyundai. ;^)
Yeah the springs I think have a tendancy to go, I've hear a few other stories with one here and there going, I think one the waist failed to turn properly. My guess is people playing want to really try and pull these things back too far causing them to snap or break. I don't play with mine, so I don't have a first hand account.
Funny, they just don't make toys like they used to. Either way, it's still a pretty fun line. I'd somewhat expect with a toy of this nature some wear and tear would occur, and expect some to break from time to time.