Emulator

inspecting gabests implementation in GSDX might be of more value.

Just an update about this...
The latest Nvidia beta drivers have driver support for FXAA.
http://www.nvidia.com/object/notebook-win7-winvista-64bit-301.24-beta-driver.html
Tested them here and driver level implementation works fine with all backends and without issues in Dolphin.

FXAA works across GPU vendors, but only nVidia has a toggle for it in the driver settings application. So having to rely on the driver settings for this is unacceptable.

Ati has a similar implementation that works too, MLAA. Until recently Nvidia was lacking in that field but now both vendors have an antialiasing implementation that is not very taxing for the GPU with good results.

Is MLAA as performant as FXAA? I've been seeing conflicting information regarding this (http://www.hardocp.com/article/2011/07/18/nvidias_new_fxaa_antialiasing_technology/5 vs http://www.techspot.com/review/436-deus-ex-human-revolution-performance-test/page6.html), but there's a mostly uniform opinion that MLAA is generally uglier.

Activating and disabling it through the driver settings will also be kind of an hassle because you won't always be able to emulate at the same settings, depending on the game, and you'll have to constantly change the application setting. Doing it through the options dialog or through a hotkey during emulation would be preferable.