Never had a problem with my mods personally. People at my dealership are actually kind of interested in them.
Here's the deal; there are federal laws that state that a dealership CANNOT void your warranty simply because you have aftermarket modifications on your car.
The meaning behind "this voids warranty" really is a way of them saying that they do not warranty the aftermarket part(S).
Just don't go altering the vehicle, i.e. Nitrous, or Turbo, FI in general.
Isn't there a stickied thread about warranty in one of the threads