*Knocks on wood* Luckily, I haven't smashed a saw under anything. I try to make sure that my dogs aren't set once the kerf starts to open up.
My big oopsie involved one of my climbing saws. I lowered my 192t down to get topped off with fuel/oil when I was climbing a cedar...once I raised the saw back up, a series of unfortunate events transpired. I somehow had neglected to clip the end of the saw lanyard on and when I went to hook the lanyard ring on the hook on my climbing saddle, I missed.
The saw went straight down, probably about 70'...not too much damage(deep loamy soil underneath the tree,) just some cracked plastic. I actually raised it back up and finished the removal. I learned my lesson to be more cognizant in the tree and to confirm that my hardware is secured anytime I manipulate it.