Spending money on an SSD is a little like buying a Ferrari to drive in New York City. You'll beat all the taxis to the next stop light, but you won't get home more than one traffic light faster.
They are expensive, have a tiny impact on gaming relative to their price, and should not be used if they cause a budget constraint. You are *far* better off buying a $75 Samsung Spinpoint F3 1tb HD for "C", and putting the remaining money into gpu, cpu, or your pocket.
Having said that, its really nice to get Windows up quick, and WoW loaded when I am late for a raid