Take a look at my signature for my machine's specs. I'm noticing something I find to be counterintuitive. When running my MBP in clamshell mode with my 23" ACD connected, overall graphics performance is sharply reduced. The dock animation is choppy, windows opening and closing are choppy, opening stacks from the dock is choppy, etc. This is when running one display only, the external ACD. When I run my setup as dual display, using both the built-in MBP display and the external (non-mirrored), graphics performance returns to normal and is silky smooth. This seems strange to me because by doubling the load on the GPU, I get much better performance. I see no difference in either scenario by toggling "automatic graphics switching" on or off. Does anyone else experience this same thing, or have an explanation or solution? I use the dual display setup more times than not, but I'm curious why performance drops off so dramatically simply by closing the lid of the MBP and using only the external display.