Can multiple Wii balance boards be used at the same time?
There are currently no games supporting multiple Balance boards, and I don't expect there to be any, if only for the price of the devices, and the amount of space needed for such a setup.
All current games supporting multiplayer with a single balanceboard do so in a hot-seat style. (or should I say hot-board)
Technically, for as far as I can see, the Wii itself is perfectly capable of supporting multiple balance boards, but I don't know if this functionality is even availble for developpers