Minimum Graphic Card Requirements
Here is a rundown on the various Unity features supported by different generations of video cards.
(This is a WIP and is very incomplete and messy, based on my very preliminary and sketchy research. Please contribute by clarifying, correcting, adding items or cards, and formatting. Thanks! Steve)
Pixel shading 1.0 & 2.0 supported by 82915G/82910GL and above Vertex shading 2.0 in software for DirectX supported by 900/950. (Does that mean it's driver dependent or game code dependent? How is Unity doing on this front?)
Render to texture render to texture support (GeForce2 or Radeon 7000) (seems to be safe to use for critical game elements like compass)
AO leaves Vertex shading (GeForce 3/4 or Radeon 8000) (Shipping Nature Renderer version will presumably fall back to less demanding version.)
Glow, Blur Reflective water OpenGL Pixel Shaders 1.0 (GeForce FX 5200 or Radeon 8500) (Will be fairly widely visible by decent non-Intel cards. Should fall back to flat color.)
Noise, Color correction, Edge detection, Sepia, Grayscale, Twirl, Vortex, Refractive water OpenGL Pixel Shaders 2.0 (GeForce FX 5200 or Radeon 9500 or higher) (More demanding. Don't assume users, especially with Intel cards, can see it.) Refractive water shader fallback doesn't seem to be working on some cards (Intel?) as of 11/21/06.
Nature Renderer Heightmap terrains? Tree LOD? Grass Bushes/Rocks