For me changing from the gnome-screensaver to the xscreensaver worked.
I still have around 7% of CPU usage from compiz while the screen is locked, which in my opinion is still a lot for displaying nothing, but at least it consumes less battery on my laptop.
I am running Ubuntu 12.04 on a HP EliteBook 8470p with AMD 7570M graphics.
For me changing from the gnome-screensaver to the xscreensaver worked.
I still have around 7% of CPU usage from compiz while the screen is locked, which in my opinion is still a lot for displaying nothing, but at least it consumes less battery on my laptop.
I am running Ubuntu 12.04 on a HP EliteBook 8470p with AMD 7570M graphics.