Here are a couple of interesting articles on brake judder. They say that it is usually caused by excess brake material on the rotor and not warped rotors (assumes the brake components are in good shape and the wheels torqued properly).
http://www.stoptech.com/tech_info/wp...rakedisk.shtml
http://www.powerbrake.co.za/pages/tech_01_judder.htm
Some good prevention tips in the articles too.
-Matt