An article on GeForce offers a guide to how users with at least 1.5GB of VRAM can unlock higher resolution textures in RAGE, id Software's new first-person shooter, and users with a video cards with at least 3GB of VRAM, can unlock even higher resolution textures. This applies to both ATI and NVIDIA GPUs, and they offer screenshots to show the difference these changes make. They indicate that the reason tweaking is necessary to force these texture improvements seems to be the result of errors in the auto-balancer that's supposed to handle this stuff automatically:

Based on our observations there does appear to be an error or two with the Auto-Balancer - though disabled for the screenshots, the on-screen frame rate display never moved below Rage’s sixty frames per second cap with 8k textures enabled, so why does the Auto-Balancer need to utilize lower-resolution assets? Perhaps it's overly-conservative to ensure that the frame rate never fluctuates? Regardless of the reason, the lack of detal is especially noticeable on the speed limit sign to the right and the ‘Loft Finder’ billboard above the collapsed building.

As mentioned, we visited other areas of the game also, primarily to judge the veracity of our results and observations. In outdoor areas packed with detail the results were identical, but in enclosed areas, such as the Mayor’s office in Wellspring, there was absolutely no difference between any of the three detail levels. In larger enclosed areas there was a difference in visual fidelity, albeit to a far lesser extent.