Ahhh, O.K. Well, I don't have a lot of Crossfire experience but it honestly seems like a waste of money unless you're going to be running high-resource-using games. In all honesty, some games utilize more CPU resources than GPU resources (CounterStrike is a good example of this). I would also suggest not using Crossfire if you run multiple monitors. I run dual-GPUs but I have no intention of running Crossfire since I run three monitors. Anything you have running on the other monitors will take performance away from your primary monitor, regardless if they are bridged or not.
Anyway, to answer your question, part (half?) of the load will be transferred from your master card to your slave card under GPU intensive situations (load-balancing).
