Anyone have any Pinewood Derby tips/tricks?

One trick my dad and I always used was to carve a notch for the weight out of the bottom of the car, about 3/4 of the way towards the back, stick the weight in, and then use modeler's putty to smooth it over. I have no idea how the weight is attached now, being that its been a dozen years or so since I was in cub scouts. Don't put anything that sticks up on the car either, believe it or not there is still some aero that comes into play at this scale.
One of the fastest cars we made was a Viper GTS coupe, almost perfectly carved, and never beaten. But then we built a '69 Daytona (used plastic model sheet for the wing)...and put an estes model rocket engine in it (started with A size, ended with D size)...that one never touched the track and still won by miles haha. I know they're kicking around the garage somewhere....