Generally if you are sending something more than 10 times per second, you're doing something wrong. Think about it... if you have 2 players, that becomes 20 packets per second in, 20 packets per second out. If you have 4 players, that becomes 40 packets per second in, 4*10*3=120 packets per second out (10 per player, has to be sent to other players, so 10*[playerCount-1] for each player). With 10 players that's 10*10*9=900 packets per second out. With 100 players you're at 100*10*99= 99,000 packets per second sent out. You see where I'm going with this? This is why in the car example I have a frequent input sync, and an infrequent position correction sync. In a serious game you'd also use some form of predictive logic in order to cut down on the number of packets. If controlling via a keyboard only instead of a joystick it becomes much easier as you can then sync button press states instead of input axes.
