I've been getting this on my (single) GTX 460, always with latest drivers, since beta. It doesn't matter if I run full screen or windowed, with v-sync forced or not. I also tried forcing v-sync with D3DOverrider and playing on my TV but it makes no difference.

For me the line always appears at the bottom of the screen, then crawls up towards the top of the screen. I tend to only notice it when I'm running forward for an extended period of time and go up or down a slope.

I also get weird ghosting effects. It's most commonly noticeable on edges near the sides of the screen when the character moves rapidly, but from certain angles I can see it on moving objects even when I'm completely stationary. One example was the dancer in the miner's guild: When looked at through 3rd person camera it looks fine from all angles and, presumably, distances, however, when I get close enough and switch to 1st person camera, her whole body starts ghosting and tearing very badly. It's not an artifact issue, the frames just don't sync properly.