Another necrobump. I just bought a UN40ES6150 (6100 series) and after applying the calibration on lcdtvbuyingguide.com, I decided to go with YCbCr instead of RGB out of my Panasonic BDT215. With the 10pt white balance settings from their reviewer, and Color space in Auto, I switched on xvYCC to see if it "increased detail" as Crutchfield says, or "expanded the color space" as Samsung claims it would. Nope. Only saw a diminishing of color vibrancy in some day and night scenes (e.g. the belly dancer at the gypsy camp) from the FROM RUSSIA WITH LOVE BD. It was a bit like switching from Warm2 to Warm1 or Standard (things get colder, blue shades are crunched, faces lose their "flesh" appearance). Blech.
Since nothing I have really outputs xvYCC, I think it's still a needless feature in search of an application (or dumb users?).