Have you followed WoW ? (World of Warcraft)
They are using a similar approach, where what you see is not the same as what everyone else sees, and its having rave reviews.
I truly support this idea. I thought this was the way it always was... haha.
So what happens when a client turns off gibs on q3a normally? I know you see a performance increase, but does it actually effect the server as well?
The only thing that i could see being a semi problem would be if you want to have a player hit by shrapnal. But even then, you could always do a double roll. One for the client and one for the server. I would think with the client side one could do actual debris calculations and it would allow you to avoid it, and on the server side, just do a distance from explosion vs probability of getting hit at a greater distance. ( something like a curve )
Since the server knows your life, it can accept the client telling the server that you are damaged more, or ignore it if the server rolled that you were hit.
and if that isnt good enough because of fear of cheats, then just the effect and sound of getting hit, by a debris would be client side, the damage would be calculated server side. so in effect you could be hit by debris and not take damage, or be hit by "really small" debris and not know your hit. (kind of like being winded, or struck out of the blue)
I mean when is the last time you actaully saw a piece of shrapnal hit you? Most likely you just look down after it feels like someone punching you and you are bleeding.
on that part i think you could get away with a lot of stuff and make it generalized, but with awsome effects.
even simplifying the debris on the server side if you wanted chunk debris, (or multi part explosion) but dont send it to the client for rendering. Just allow the client special effects to be shown, and then register a hit to the client "if" the server side debris hit the client.
The only real way to avoid shrapnel is to dive behind a wall or something. (or someone ;)
-s. bob