Yes, but the masses they are talking about climing up and down the elevator are nowhere near large enough to have massive impacts... plus in some designs that I saw there are 2 cars, one climbing up the ribbon while the other climbs down.
If this is true, then its just a matter of adjusting the decent of the empty car with the loaded car to keep the center of gravity on the ribbon constant. Not a simple task, but not an impossible task either.
It would be cool if they had one of these in Alaska, it would be going up at a low angle along the earth.