Q u o t e: It's very likely that magic find (MF) will be restricted to very specific uses. It would work on a per player basis, so if I have some MF it would affect what drops I see and not yours. For the sake of co-op we don't ask that you damage an enemy to receive experience or drops, only that you're within a close proximity. Asking every player to damage an enemy in order to receive experience or loot encourages really disruptive behavior that undermines the intent of co-op. So the situation being described could be a problem, but...
As I said it's probably going to be fairly heavily restricted to specific sources and amounts. As an example, completely hypothetical, let's say that the only magic find available is from placing a diamond gem in a head slot. It's useful because of the amount it provides, but maybe other gems in a head slot provide things like bonus XP, bonus gold, etc. Then it's not a choice of power vs. MF and building characters around the system, but a choice between interesting bonuses that will probably change through the career of a character. Anyway, that's just a thought on how it could work. It's still under consideration. We like the idea of having some way to improve your chances to find magic items, but not as a driving statistic for characters.
It's also worth pointing out in this case that enemies in Diablo III are more sophisticated. You'll find them targeting characters in your group they perceive as weaker, keeping distance, and cooperating to try to kill you and your group. So having one person run ahead to face pull everything, let alone be able to solo everything in a multiplayer game, probably isn't going to work out too well.
Better than the "MF character feeds your real characters" paradigm.
So there may or may not be a slot/gem combo that only does weird non-power related bonuses? Like, it can never have attack, precision, defense, etc, only MF, gold find, XP bonus? What about gem finding or rune finding?
Earth or somewhere like it.