There won't be a 360 or PS3 port so can we stop talking about them? Please?
My battle-weary XPS Gen 2 w/ 7800 GTX actually plays the SP demo reasonably well with decent settings after some tweaking, OC'ing and driver upgrading.
Main thing that taxes my system are the volumetric clouds in the opening scene with the plane, HDR, and physics. If I set volumetric to Low, Shaders to Medium, and Physics to Low, I can run everything else on medium playably (15-30 fps) at 1280x720. Plus I have added a few VERY nice graphical tweaks you only get at Very High in DX10 normally:
Using Notepad, create a file called system.cfg in your Crysis SP Demo folder and add the following:
con_restricted = 0
This enables Parallax Occlusion Mapping (POM -- gives depth to certain textures such as the stream bed going up the hill to the final checkpoint), and volumetric light shafts (a.k.a. "god rays", beams of light and shadows that are most noticable underwater or looking through foliage into the sun).
I might do some comparison screens later.
edit: actually you need to use High Shaders to get those effects but you can still disable HDR with r_HDRRendering=0
edit2: here's some comparison pics from DX10 with POM and god rays (note I did not take these):