I was watching a DVD on my PC via Windows Media Player (WMP), which I rarely do, and noticed some odd on-and-off vertical banding and poor (meaning too bright) blacks. Thanks to a search engine I was able to find root cause of the problem in under one minute: I guess I was lucky this time? The vertical banding was indeed caused by the Enable dynamic contrast setting in the ATI Catalyst driver for my Radeon 4850 video card. Can you imagine finding the right setting among one million without the power of search?
People seem to report that VLC does not show the banding artifacts, but that is not an option for me since WMP takes full advantage of GPU hardware decoding (CPU load near zero percent), while VLC uses the CPU to perform the decoding (over 40% CPU usage on my E8500).