Baseline (Widescreen) Solution & Issues
Native support for widescreen resolutions. Please note that the game will use the aspect ratio of your current desktop resolution. If the aspect ratio of your desktop resolution is different from the aspect ratio of the in-game resolution there will be stretching.
Ultra-Widescreen (21:9) Specific Solution & Issues
Eyefinity / Surround Specific Solution & Issues
Native, anamorphic : gameplay, cut scenes and menus are pillarboxed in TripleHead resolutions. As reported by cranky, make sure your desktop res's AR matches your desired res's or the game will stretch/squash.
5040x1050 is unsupported, probably because of the refresh rate; I suppose the 60 Hz trick revealed by mattsimis could circumvent this limitation, but fiddling with custom res's does not work very well with WTH on my setup so I can't be sure.
4k UHD Specific Solution & Issues
Stereoscopic-3D Solution & Issues