Closest I've come to whiping out big was when I got the bar jammed and ended up lifting the entire rack off the floor. A bit more weight, not to mention the balance issues, then I was prepared to deal with. Didn't break anything, but I wasn't moving too spry there for a while. ***knock on wood***
Careful of the back. Sam's Club has one of those massage loungers for around $200. Highly recommended. Gotta tie my wife up so I can have my turn in it.