I'd like to suggest implementing Color Managed video playback as a feature. It has previously been suggested for image/cover-art display, and indeed that would be nice, but implementing it for video playback would be brilliant.
Currently, Media Player Classic Home Cinema has implemented this feature. They do the transformations on the GPU. It plays back glitch-free; works great.
I've tried it out, and the results are AMAZING. Robin Hood (the Errol Flynn version) takes on a realism it never had, instead of the cartoonish colors so often seen with too-vivid computer displays.
This feature would be especially helpful for those people with wide-gamut displays, which tend to over-saturate when showing non-color-managed material.
Those of you who have a wide-gamut (30-bit color) display, or a color-profiled monitor, I strongly suggest you download MPC-HC and take a look. You'll be shocked at how much better it looks.
Obviously MPC-HC is not really a competitor to JRiver... If this could be implemented in Media Center (there's no reason why not) it would be the only application of it's type to take such a dramatic step in improving video quality.
Some info on how they've implemented this in MPC-HC is here:
http://voxelium.wordpress.com/2010/09/20/icc-color-management-in-media-player-classic-home-cinema/Thanks,
-Will