New Poll - OUCH!

Excellent points, Stephen. Sorry about those horrendous injuries though!
With regard to where to draw the line, I can only (once again!) bang my stage combat drum and talk about a particular preventative measure which I like to use as a Fight Director.
In the final build up to opening night, once the performers are quite familiar with the whole fight moment, I encourage and aid them in creating a "bail-out" device. This can be either a word/phrase or movement which is a kind of secret code between the performers involved. If one of them becomes aware of a potential accident, the bail-out device is employed. For example, if the bail-out is a word, then its a word that the performer can say, but still sound like they are in character in order to warn of potential danger without breaking the illusion. Similarily, if a movement is required, I often use a hand squeeze or some sort of physical contact between the performers when a vocal bail-out wouldn't be appropriate.
What is ultimately done as the bail-out depends on the particular needs of the performers and the production, but the principle is the same. Safety first, and give yourselves a chance to avoid danger. Of course, the bail-out only works if the performers are aware of the potential danger, but then we're back at being human again.
I think its largely possible to prevent an accident without breaking the illusion, but at the same time, accidents will still happen. Also, people's "pain-thresholds" are different, and whilst you managed to carry on in what I would consider extreme circumstances, others might well have reacted differently. OUCH indeed!
Play safe everyone,
Andy Fraser
Fight Director.