Here's a link to a story about John Long getting injured at a gym when his bowline came untied and he fell.
John says the knot failed because he didn't finish tying it properly. I used to tie in with a bowline because they are easier to untie. I no longer do because a friend of mine was 50 feet up a 5.12 trad lead, noticed his bowline had come untied and wouldn't hold a fall, had to re-tie the knot with one hand while barely hanging on with the other, and then lowered to safety. I know it's a safe knot when done correctly, but that is two people I know of that are much better, harder, and more experienced climbers than I am that have narrowly escaped disaster because of a bowline coming loose.
I've decided to just stick with a figure eight. It's never come loose on me, and trying to untie one after a hard fall just gives my arms a better workout. Nothing wrong with that.