It wasn't as bad as I'd feared, to be honest, although a comment one of our coaches made once to the lines of "you want your chain to move smoothly like this [ergs], not jerkily like this [takes a couple more strokes]... hmm, I can't actually row badly enough for it to do that" seemed amusing in the light of the guy whose chain almost seemed to be slack by the way it was whipping around on the recovery.
I wonder if they'd let me turn an erg around so that it was facing a wall...
I honestly don't understand how the ergs moving is not a major problem: my erging strength is very bad for a rower, and I doubt it's even average for a fit, strong male who doesn't row, so how come they haven't secured them in place somehow following other people causing this?