Check out the crappy counterweight on this aluminum driveshaft (pics inside)

[~The Jester~]

Although a little better than the pics you posted, mine is still nothing to get excited about. On the diff end, my "chunk-o-metal" is smaller than yours, but still welded in the middle. It does look like someone attempted to make it round at least.

On the transmission end, my chunk-o-metal is nothing but a huge flat washer. Here again, just welded in the middle, but a half a$$ attempt was put forth to make it round. The quality control guys need to put down the coffee and newspaper and pay attention over there. I was working on an 02 Crown Vic police car last week, and the driveshaft on it was the same way.

As far as the forces involved like Hissin was talking about, stop and think what has to happen just to get the car to MOVE. Have you ever tried to move your car by turning the driveshaft? It's amazing how difficult it is, yet our engines and trannys do it all the time. Every bit helps, so a good balance job is a must!