If you push the forward key in an llVehicle, the signal gets sent to simulator, script does something, result of input comes back.
What I'm trying to say is vehicles in SL have latency that other multiplayer games don't.
If the client can be told basics about the llVehicle it could be making a good guess about what the vehicle should be doing before it gets a definitive answer from the simulator, thus making vehicles appear much snappier as the result of input would be instant client-side
Or perhaps even make it possible for a client side script to be authorative on an objects position and run the physics simulation client side, just sending results to simulator for other residents to see?
(I'm currently just throwing random ideas out there to see what sticks, sorry if my posts seem excessive)