Alec and myself are busy playing Rage, and rather enjoying it, actually. That said, we had to do quite a bit of tweaking to get the damned thing working ok. We both used the fix detailed here in combination with enabling the GPU transcoding thing, while also updating drivers (particularly important for ATi cards). This seems to address most of the texture pop-in issues, and apparently ups the texture res, too. You'll ideally need a card with 1.5gb VRAM to get a step up in texture quality, and if you have 3gb or more it's reportedly possible to go higher still, although this article on the Geforce site said they found no immediate differences. Anyone with enorm-VRAM able to confirm?
Bethesda echo these and other fixes here.