this is actually not a real 'problem', just an annoyance:
I use mplayer to play my videos on my main screen and on an attached 32" LCD TV. Problem was, that the resolution of my main monitor is higher than the one on the TV... so I used mplayer's -xy option to resize the videos accordingly (mplayer -xy 1366 -fs -ass Video.mkv). But now, every time I play a video file just on the main monitor, it gets resized to the 1366ish resolution whenever I switch to fullscreen! Leaving the rest of my screen black, or with artefacts in the lower right corner .
When I start the video with mplayer -xy 1440 (my native resolution on the main screen) it gets resized correctly, but when I switch to fullscreen it gets squished to 1366xXXX again.
And now, every time the screen gets 'dimmed', e.g. when I'm asked to input my password to start an administrative application (e.g. the package manager), Mint only dims a 1366ish portion of the screen.
Turing of compiz solved the 'problem', but I really like eye candy, so... for now I'm using vlc to play videos on my main monitor and mlayer when I want to watch movies on the big screen. (Yes, vlc plays the files in 'full' fullscreen, even when the the video output is set to xv.)
Another workaround is to set mplayer's video output device to x11 instead of xv (but x11 doesn't support hardware acceleration).
nvidia-glx-177 (177.80-0ubuntu2) drivers, from the official Ubuntu repositories, on a GT8800.
Twinview enabled, set to clone
Got this with LinuxMint 5 and the new RC1.