Edit 19/05:
Some users have reported better performance by renaming the executable file of the game (witcher2.exe - located in witcher2/bin folder) to fear.exe. I have tried this myself, and it does improve the FPS. However, it also seems to cause more flickering on my system. Worth a try! :)

Okay, so AMD does not yet have crossfire profiles for the Witcher 2, so if you got either two Radeon cards or a single card with two cores, you can probably expect some stuttering and/or flickering at certain scenes. Temporary fix: download this, which will allow you to force other crossfire profiles for the game; might or might not work with your setup, experimentation required. Secondary fix: disable catalyst AI (in your catalyst control centre) - might improve performance at cost of quality. Tertiary fix: pull out one of your cards.
The best solution: wait a week or so until AMD got an official profile up. Crysis 2 took about a week and a half or so, so I it shouldn't be too long. Until then, at least play with that uber-sampling feature turned off, that's a giant performance-hog right there which doesn't really improve quality all that much.

Right, back to playing. Even with the wonkyness with the graphics, I'm still having a great time! A part of me want to stop now until I have everything fixed, but another part of me really don't give a damn about the graphics and want to keep on playing for the story and gameplay. That's strength right there. Yup.

Oh, and I bet we can probably expect a tweakguides feature before long. Early days now.

I am not back home yet, I've had a similar situation with another game last week (Hydrophobia) and the meanwhile fix was easy: I renamed the executable to fear.exe (yes, this horror shooter from a few years back) and my FPS instantly jumped into awesomeness.

I wonder if it works for W2 too?

And what can I do with my HD 6990 since am forced to play in windowed mode? Crossfire is disabled in this mode so AMD profiles won't help much, first need full screen mode, patch for mouse inversion and to uncheck smooth mouse, etc. Amazing game with jaw dropping graphics though... Sapkowski would be proud ;)

You can set fullscreen mode in the game launcher, look in the "Video and language" section (not in the game itself, but the launcher-program that opens before it). :)

While the option is there the game won't start in full screen mode for me only once I switch to windowed mode ... :(

About the 2 core cards, i believe the game is using the 2 cores i have a 5970 and i maxed everything (didn't try NASA uber sampling tho lol) and the game runs extremely smooth , must be using the 2 cores i believe

Try going to the bin/config directory your Witcher 2 install folder, say: thewitcher2/bin/config look for a file called "user.ini", open it in notepad and make sure the fullscreen option is set to "fullscreen=1".

I don't have that particular card myself, so I can't test it. But it might help. Same card that I have. I am just trying various ways to get everything maxed out, just to prove that I can. :P
It isn't really all that important, but it is fun. I do experience some flickering at times and sudden drops in framerate at certain places, but usually it is quite smooth indeed as long as I disable the uber-sampling feature. Still, it only uses one core as far as I know, there are no official crossfire profiles at this time.

"And what can I do with my HD 6990 since am forced to play in windowed mode?"

Seems I read when that first came out it was always going to be an issue for crossfire until profiles would arrive same with SLI its the nature of the Beast!!!

Ohh ty for the info mabe when xfire is enabled the game will run even better , i do have some weird lag when blocking with "E" dunno if it is my timing but sometimes Geralt just refuses to block lol. And on the menus i have a small weird lag. I was looking at fraps and i get 60fps but sometimes drops to 17. Lets hope for a fix for the 2 cores , i will bookmark the thread , ty again :)

My average FPS went up by ~15 by renaming witcher2.exe to CompatAFR-1x1.exe. I think this is the same as forcing one of the general crossfire profiles in radeonpro. I haven't played long enough to see if there are any negative effects but it looks fine upon loading my save.

Hmm that is strange. I have 2 4870s and I thought they would behave similarly to 4850s. No flicker for me and gpu usage is 60-80% with fps generally between 30 and 60 (vsync capped, in the pre-dungeon escape areas). I'm using a mixture of ultra and high settings at 1680x1050 with catalyst 11.4 drivers and 11.5 CAP1 profiles.

http://twitter.com/CatalystCreator/statuses/70598955150479361 Confirmed they're looking into making a profile.

Ty very much for the info.
And guys i am using Catalyst 11.2 anyone using 11.5?

Using Catalyst 11.3 here. I'm owning a HD 5970 , all settings to highest except the one above "Vertical Sync" (can't read it, is overlapped on my system due DPI settings) which causes substantial FPS drop.

Anyway. Cutscenes at the beginning: witcher2.exe -> ~ 55 FPS. Creating a copy named fear.exe -> 75 FPS. Yay! Usually the FPS are around 60 later, sometimes drop to 40 but it plays well.