they get unloaded? Hmm, I'll have to look at this, see what happens, or do you loose the cart?
I know if you hit the end of the rendering range and get stuck, you loose track and the cart :P
Mine carts seem to follow the principals of magnets, when you run 1 into the 2nd, its like 2 NN or SS poles of magnets coming into range, they come close then push off, I guess thats the principal of a booster, the booster range is only 1 block, so it will boost an adjacent cart on the next block/track, but not the 2nd track across, mind you, a track that runs opposite to the direction of track 1, and is adjacent, will hamper carts going in the other direction
Incline seems to be 1 full block wide by the same high (45 degrees incline)
you can use a forge inside a cart to make the cart powered, but a powered cart that doesn't have fuel doesn't like being pushed
I'm interested to know how to remove the forge back out of the cart, mine is currently just pushed to the side for now.
Pitfalls, if the pit is big enough, the cart can fall inside it