GPU / Graphics
To check which GPU is currently in command (that means which is an active VGA controller) type in
lspci -vnnn | perl -lne 'print if /^\d+\:.+(\[\S+\:\S+\])/' | grep VGA
x.org cpu load high
This is a bug, either in an application that's running on your X server, or in the X server and triggered by an application you're running, or (most likely) in your display driver.
To pinpoint the culprint, start an X server that's not running any risky application.
Log out, then switch to a text console by pressing Ctrl+Alt+F1. Log in, then run
sudo service gdm stop startx xterm -e top -- :0.
If the CPU load increases, then your driver is the culprit; otherwise it could be either an application making repeated requests to the X server or a bug in the X server. If you can't see any application using up CPU time, the X server is likely to be the sole culprit.