I am one of those who has complained (here) about the problem. Ultimately, I decided not to send it in for repair, because otherwise, things were fine, and I was worried about getting one that had other problems which were being reported at the time. For me, the problem is most evident if I try to take a picture of a rectangular frame centred in front of the camera. This can drive me insane. There are also problems with straight on architectural photography. In that case, however, since except in hurricanes and earthquakes, most buildings don't move much, a check with the screen and a retake usually solves the problem. To be honest, though, I don't really know how severe the problem is, because I have taken pictures with my OM or my Mamiya 7 that I thought were level when I took them, but were not. For instance, using the 43mm lens on my Mamiya, there were times when looking through the external viewfinder I thought at first everything was level, but the handy level in the viewfinder told me I was way off.
When shooting buildings, I tend to leave a little room for slight rotations in Photoshop. I am also wondering if the problem I referred to in shooting frames, which would be at relatively close differences, might be a parallax issue. That is, although I think I have centred things, that isn't really the case?
In the normal course of my shooting, I have not found the wacky lines to be a problem. I would send it back if my main area of photography was architectural, or if there were other problems as well.