I've rendered out a mov using H.264 at the standard High setting. On my Mac it looks perfect. When viewed on a PC running Windows 7 via Quicktime Player, not so much. It looks very blocky in the blacks, with everything brighter and washed out, and with low saturation to the colors, as though the gamma has been lowered. Checking the "use high quality" setting in Quicktime Player does nothing to help. Now, when the same file is viewed in WMP, it looks close to how it does on the Mac.
What gives? I thought that Apple had ironed out most of the Quicktime gamma issues. This is exporting from the latest version of FCP, and viewing in the latest version of Quicktime Player for Windows.