Hey Dan. I think you know I'm an electrical contractor. It's a family business so I've been around it my whole life.
We work in hot panels far more often than dead ones. Usually shutting them down is not even an option. There are guards on breakers and terminals that protect somewhat from touching places you shouldn't. If you know your way around a panel and pay attention to what you're doing, it can be done safely.
I actually don't remember ever getting shocked in a panel (plenty of shocks in junction boxes and outlets). I did have a small arc flash in a panel one time. I blame the jerk that originally wired it for that though. The panel was a complete mess and I had to move some wires around to make room for the ones we were adding. As soon as I did, a wire pinched and shorted against the panel and went off like a welding arc in my face. My reaction had me flat on the floor. And I never even got shocked. Just a lot of black soot on one hand.
The voltage in a panel is the same you'll find in the outlets around your house so a shock would be the same. The real risk is arc flash because of the high current conductors. Search YouTube if you want nightmares
Be safe. I don't recommend that anyone works in a hot panel.