From time to time, a black horizontal line flashes across the screen, usually in the upper third (at least when I noticed), seems to be random. Looks like a GPU driver issue (maybe NVidia's fault?) because it appeared first with the JB updates.
Seems like it is on the top third of the screen indeed. I also think it might be (Tegra) drivers related...
Still Asus should be able to fix this!
Maybe we should all start a facebook page and like it, send it Asus so they know just how many people are taking the black lines as a serious issue!