The biggest "Oh shit!" moment would have to be when I moved from Boston to Missouri. We started to wheel my Star Wars cockpit down the loading ramp into my shop when I realized the ramp had walls that were too high for the wheels to work. While I was trying to think if I had some heavy plywood to put on top of the ramp, my brother grabs the heavy end, says "come on, we got this!" and starts walking backward down the ramp. I'm like "AAAGGHHHH NOOOOOOO!!!!!!" but he wasn't stopping. So I, with my skinny-ass 125 lb. self, have to grab the other end.
Oh. Shit.
We carried that heavy @#$@!! Atari cockpit
*IN THE AIR* the length of the truck, down the ramp, and into my shop, around and through the funky corner entry, and then set it down. Gently. It was about 40 feet of "Oh, Jesus, this is the day. See you in a few!" agony.
As soon as we set it down we started thinking exactly how to DIE. He sat down with a mixed drink, took one sip, and almost passed out. I was lying in the grass, pant-sobbing, and cursing Atari and their 800 lb. gorilla cabinets in every way I could think of.
Damn! F-U Atari!!!
But oddly enough, cabaret cabs have given me the most scares.
I was moving an AD Deluxe mini down the (wet from rain) outside deck stairs when it got away from me. I wound up on my stomach getting dragged off the deck with only one hand on the dolly. My fingers got it pretty good when they broke the edge off the steps. Yeah, step
S. My hand went through 3 of them.
Scariest thing I've witnessed was when my girlfriend and her son were moving a Ms. Pacman mini down some concrete steps. He dropped the bottom end and she narrowly avoided the machine coming down with her between it and the steps. That was HORRIFYING to watch. But at least there's an endless supply of "my girlfriend vs Ms. Pacman street brawl" jokes now.

And she still helps me move the machines! She's a definite keeper.