No, as mentioned earlier in the thread FSAA renders the scene ONCE at a very high resolution then scales it down. According to CDPR's description of ubersampling it renders the same resolution frame multiple times and then composites them somehow... the question is how, since there must be some jitter or something to ensure that the frame being rendered multiple times is not identical and thus not helpful.

No, that is different; what you are calling FSAA is actually supersampling. Supersampling would permit more complex filtering as the image is downscaled; for example, a sinc or Lanczos filter.

FSAA as originally described renders each pixel 2, 4, or more times at offsets of +/-1/N pixel. It does not render the image at a different scale. The only difference between FSAA and the way Ubersampling has been described is that Ubersampling renders the entire frame before filtering, rather than working pixel by pixel. This may be computationally more efficient on massively parallel GPUs at the expense of requiring additional memory for the complete frame.

FSAA reference, with comparisons to other AA methods: http://homepage.mac.com/arekkusu/bugs/invariance/FSAA.html

Either way you compute it, it's a first-order moving-average filter, nothing more, and there are far better ways to do antialiasing.

"Super Sampling anti-aliasing (SSAA),[2] also called full-scene anti-aliasing (FSAA),[3"
http://en.wikipedia.org/wiki/FSAA#Full-scene_anti-aliasing

And yes, the link is sourced. You can find like 20 other references also if you try Googling it yourself.

I have a single card and Ubersampling works fine.

There is no single GPU that can run The Witcher 2 maxed with Ubersampling On at a good framerate (30fps or more). Not even the GTX 680 can do it.

You need GTX 470/560TI in SLI minimum and I can definitely tell the difference on my single GTX 470.

Everything looks much smoother but I'm wondering if AA couldn't have been implemented in a more traditional way with small steps like 2x, 4x, 8x, 16x etc.

It seems to me that Ubersampling is applying a lot of AA which kills the GPU even though it's not necessary.

Ubersampling is a "dumb" brute-force form of AA. Effectively, it doubles the GPU's workload. The game has other less taxing AA settings you can use instead. But don't force AA through your GPU's control panel; the game does not get along with forced AA.

I got a solid 30 fps with my GTX 680 with the basic clocks. There is probably some part of the game which that can drop i presume, but most of the time it's 30.

I suppose "ubsersampling AA" use the Full Scene Anti-Aliasing which calculate a higher resolution of rendering & then adapt this high resolution rendering at your monitor's resolution.

That's why aliasing disappear & everything is sharp & soft.

Too bad we can't specify the MSAA (2x, 4x, 8x, etc..) & FSAA lvl from 100% to 200% (where 100% is your standard monitor resolution).
ArmA 2 got all these options & it's pretty cool to adjust the rendering to the GPU capabilities.

But with DX11 next generation game (Witcher 3), all this gonna disappear.

I get 30 with an overclocked 670gtx on uber. Switch it off its a solid 60fps.

I was finally able to run the game at playable FPS (30+ FPS at all times) with everything maxed and ubersampling enabled at 2560x1600.

All it took was GTX680 4GB SLI. :-/