I'd like to say close to a hundred, if not over. At least 30 sets of dice, still kept in their chessex containers, the rest in a blue bag the size of the ...er... sacks you see hanging off the back of certain pickup trucks.
Most of the gamers that I've played with usually only two or three with them at a time, but wouldn't have any problem getting a hold of 10 or more for a game - or would just pool their dice and pass 'em around.