Update: the correct optimized AMD driver is available here. It's Windows 7 only and provides benefits for the 4000 series, not just the more recent ones. Note it doesn't contain the Battlefield 3 optimizations, if you're playing that as well. The 11.10 set, expected to launch late this month, should merge both.
Update: reader 'qqless' reports NVIDIA users may have luck with the pop-in by forcing AA, AF, V-Sync, and triple buffering in their control panel. AMD users may want to tinker as well. Other workarounds can be found here.
Quite a lot of people are suffering major issues with the PC version of Rage, including awful framerate, severe texture pop-in, artificating, poor mouse control, audio stuttering, crashes, and more. Some seem to be running well enough, however, but if you're considering buying, we recommend you hold off for our PC-centric review, expected later today or tomorrow; our PS3 review will be up any minute now.
For those that are experiencing major issues, AMD is dropping an optimized driver shortly (ignore the one available currently, as it's got its own problems), so if you're in that camp, sit tight. In either case, publisher Bethesda's VP of marketing and public relations Pete Hines says they're "actively working with AMD and NVIDIA and [developer] id to resolve the issues", so there's hope, if no graphics options.