I was wondering if anyone has constructed a shoulder mount for their lightweight DV camera and weighted it so it would have the mass of a regular 35mm shoulder-mounted camera (I have no idea how much they weigh. 20 lbs minimum?). I realize that lugging around the weight is a pain, but wouldn't it smooth out handheld work done with small cameras if you were going for a more cinematic aesthetic? Or is this totally off-base?

I built a simple shoulder mount for my ZR. It's easiest to just balance out the weight of the camera. Uasually if you do that, it's more than enough weight to keep it securely on your shoulder. I can't imagine adding more weight would help much.

15-20 lbs is right around an optimum shoulder-mounted weight, IMHO. You can go heavier but fatigue will become a factor on longer takes or event shooting. It's obviously a matter of preference--some "tough guys" might prefer more.

35mm cine cameras range from 20-45 lbs in handheld mode, with the preferred cameras for handheld (Arricam LT, Panavision XL, Aaton 35-3) landing somewhere in the middle, depending on lenses used.

The really important thing is that you have a truly balanced mass that "sits" on your shoulder, not relying on your handgrips to muscle into position. The better shoulder adaptors for DV cameras have the counterweight (battery, etc) situated below the shoulder to bring the center of gravity down.