Interesting. Orriginally, I had been playing with an idea of endurance and fatigue. (Personally, I *HATE* hitpoints.)
Basically, the way it would work is like this:
You would have some stat similiare to constitution. That would determine your total endurance. Now, every actuion you do causes some level of fatigue... the more often you do it, the less it generates, to a point. Your endurance is the amount of fatigue you can handle... So your max fatigue is your endurance. Now, the more damage you take, the lower your endurance becomes. When your fatigue reaches your endurance, you pass out... if it exceeds it by a great deal for long enough, you die.
Now, imagine combining this with the systems idea... or even just the basic infrastructure. Hrm... It would be interesting...