Hi
I just tried out a new Sony NS76 DVD player on our Mirai 27" DTL-527V200 via HDMI 720p. I picked a night scene from 'The Warriors' and switched between RGB and YCbCr. The difference was very obvious.
The YCbCr setting is the default and the picture was rich with good colour detail, deep blacks, full fleshtones, and plenty of shades in the dark parts of the picture.
The RGB setting gave a very washed out looking picture with the deepest blacks turning to grey, and a faded look to the entire colour range. It could be that if I totally recalibrated the LCD I might improve the picture, but I believe the adjustments would be too drastic.
I agree with others on this thread that there is no harm in trying out both settings and judging for yourself. Just make sure you properly set-up the display for each setting, maybe using the THX Optimizer on many DVDs such as the 'Star Wars' films (look for the THX logo on the covers).
Hope this helps