I am now having the same problem. I have been playing the game (Witcher 2) fine for weeks and now I'm suddenly getting very similar artifacts. I've done everything I could think of including restoring windows to an earlier restore point, updating drivers, changing nearly every setting up and down both with the game settings and with the graphic card settings, and uninstalling and reinstalling the game (which repaired a .Net library making me hopeful). But alas; no luck. There are a few areas where it doesn't occur, but nearly every area in Chapter 2 is now doing this (I had no problems when I first started in Chapter 2). I also checked some other games to see if it was a general problem with my card, but everything seems fine in other games. Oh, and I can switch to the power saving Intel GPU and the game doesn't have these artifacts. I would just play on the power saving GPU, but it really doesn't do a very good job and the game is choppy and hard to play with that GPU.
Any ideas at all?