I probably watch too much TV, but there was a CNN report this weekend about a guy having a framing nailer backfire, and a nail end up in his mouth (unbeknownst to him, but that's another story).
I can't find much on this on the Internet, but am wondering how common it is. Doesn't sound like a lot of fun if it happens. I guess when using my Senco finish nailer, I'll make sure I am not directly behind it.