Now that the single-player Crysis demo is available, I'm sure plenty of graphics enthusiasts promptly went ape to push their PCs over the limit. If you've noticed in the graphical options menu, there's a "very high" setting but it's grayed out. However, a perceptive Crysis Online forum member discovered a way to implement the "very high" graphics setting into the demo.
It requires editing the demo's configuration files (located by default in: C:Program FilesElectronic ArtsCrytekCrysis SP DemoGameConfigCVarGroups); you open each file in that folder with Notepad and do some copying and pasting. The first paragraph of various options appears to be the "very high" setting, but it's not implemented, so you have to paste the first paragraph over the last paragraph (noted by [3]) in the file.
I, of course, would recommend anyone who wants to try this to back-up all of these config files first. I've tried it myself and the tweak certainly works because everything looks much nicer: realistic water waves, tire tracks in the sand, noticeable bump mapping, etc. So if you have a beefy PC then, by all means, try this out. Some screenshots are below:

Hmmmm. Very high showed up for me.... maybe it only shows very high for high end video cards
(I have a EVGA 8800 GTX),
Yup DX10 cards on atleast dual cores should be able to get to it.
Whoa...
Showed up for me. So it must only stay greyed for low end systems.
Very High = Vista systems
Limted to high = XP
Oh, I see. I guess Vista chewing up resources isn't an issue here. =P
Seeing as the Crysis demo doesn't utilise multiple cores I doubt having a dual core is a prerequisite.