If you check the steam forums there a various config file downloads and a cache temp fix which made it unnoticable for me, basically fixing it.
http://forums.steampowered.com/forums/showthread.php?p=25524360#post25524360 - Config
http://forums.steampowered.com/forums/showthread.php?t=2156408 - Cache
Thanks for posting those.
This is a little clip I made, with no pop up. There is a frame rate drop (because I am recording in Fraps and that is taking up some of the system resource).
(Don't worry about Spoilers, it is just me taking down a few enemys, or trying too

)
http://www.youtube.com/watch?v=YTTWfR9Om-o
Running perfectly 60fps without Fraps running at the same time.
This games is a lot of fun.
EDIT: This is my take on the game for those that are asking about how good the game actually is
Been playing this for a fair few hours, and got to say, it is pretty decent. It isn't groundbreaking or earth shattering (like Quake, Doom and others in the past), but it does have some nice new features.
It is still a "corridor" shooter in some respects, but it makes you feel like your in an open world. It isn't as open as Fallout 3 for example. You can go where you like, but it isn't as "free".
The buggy thing is quiet fun, but things like this never really add much to a game for me. You get from A-B in your buggy, and you can add weapons/other upgrades to it, but that is about it. It is good, but again not ground breaking or new.
The best thing about the game is probably the enemy AI. This is where Rage shows it's true quality. The enemy's will literally attack you from all angles, and aren't just on a Kamikaze type mission. They will run towards you duck, dive, hide, jump off walls, dodge, side step, dive, all sorts. They aren't just going to hide behind walls and pop their head out at you, they move around making it harder to guess their next move. The enemy's are definitely not on "rails".
Story wise it tells you what you need to know, and I quiet like that for a change. Nothing too complex or in depth, but enough to keep you engaged and interested.
I think the general feeling (and the feeling I am getting) is that Rage is well worth playing, but you could probably get away with renting it (or picking it up after the inevitable price drop with all the big games on the horizon). Even with side quests, you will complete it in under 10 hours (some reviews claim). It wont see you rack up 100+ hours like an Oblivion or a Fallout 3.+
I doubt there will be much replay value, and the multiplayer is all buggy based (i.e no FPS death match). Maybe this will be added with a patch/update in the future (be a bit mean if they charged for it).
Rage, like many games that are delayed/in development for so long, are not "bad" games. They are just games that should have been released a little while a go, before everyone else did what it was doing. With a range of top games coming out in the coming months, Rage will be in the £20 sale pre Christmas I feel. Which is a good thing, because everyone should give it a go. Just don't expect anything too new or exciting.