I run my HTPC with a Samsung 46D6500 over HDMI to a Radeon 7750. I just upgraded from a Radeon 5000-series card.
I have a problem with a disturbance to the picture when motion is displayed on the screen.
A static image is fine, but motion in a movie or even scrolling on a webpage causes an annoying shift in the picture, the lower third of the screen is momentarily shifted in one direction, left I think....
This happens in "PC" mode. If I change to "DVI Devices" then the same thing happens, but the line is in the top half of the screen.
I mentioned an upgrade to 7750, well this problem was apparent with the old card too! Despite hard drive format and windows 7 clean reinstall.
I am using the most recent Catalyst drivers.
I also use the TV to watch TV over sat (have no standalone Bluray) - watching TV does not show any problem.
It also doesn't matter if I connect the TV directly to the PC or though my Onkyo, same results.