Sounds like all have been pretty lucky--at least compared to me. I've taken my share of touch-hole wash from the occasional flinter that I've failed to notice (and had no warning from the shooter). I DID, however suffer two somewhat freakish accidents from my own fowler!
A wee flint shard broke off the rock and flew, either from the inertia of the moving cock or from the force of the open-air ignition. As bad luck would have it, it happened on a day when my glasses were not on my face. I took it in the left eye, cutting my cornea. Not a bad injury, but it took me off to the emergency room a half-hour away, and sort of spoilt the day for the two friends who spent a few hours of bonding time with me. I don't want to repeat that one, ever.
Ever since, I don't shoot without my glasses on.
Then once, even when I was so protected, I stepped back from the line after a shot to jaw a while, and was asked why that blood was running down my nose. Me fingers found, yup, another not-as-wee shard stuck right between my eyes immediately above the bridge of my glasses. It was about 3/16" square, and very thin and sharp, embedded right between my eyes. Just a little cut to my already somewhat scarred face.
So it's not the flash of burning powder I've come to respect when shooting a flinter, it's the durned rock shedding little pieces!
I wear earplugs too. My wife says I'm deaf enough already.