How does it work? It works strange in 1.2 - UberSampling = 1 (manually set in User.ini) works faster than UberSampling = 0 (turned off) - 30-40 fps against 15-25 fps, and UberSampling = 2 (turned on in configurator) reduces fps to 5-10 ...

This is odd, after the 1.2 patch I set ubersampling to 1 from 0 and it has improved my framerate, got rid of the stuttering, reduced the pop in and improved the visuals. All very strange.

i7920@3.4GHz/6GB DDR3/5870

Has Ubersampling=1 increased the visual quality? Does it look any better?

It looks better to me, no jaggies at all and textures seem sharper. Apparently Ubersampling is....
“The whole scene is rendered multiple times to give best possible texture and object details and antialiasing (better than antialias and anisotropy even on highest settings).” So I guess the improvements make sense.

How many times is it rendered, if you don't mind me asking?

Ubersampling = 2 is 2x2 OGSSAA so 4 times. Analogue for = 3 and =4 (4x4 OGSSAA, 16 times)
I think it's easier to think of it as rendering at a multiple times higher resolution and using a downscaling filter.
Ubersampling = 1 is only Anisotropic Filtering, from what I've heard

I've taken screenshots with it on (1)/off and there is no noticeable difference, however it did seem to eliminate the stuttering issue and maybe even improve performance a little.

I wonder why this is not even setable in the configurator.

Framerate is the same (for me) but the game runs really smoother now and has less stuttering now when ssao is used. I'm really impressed.

I reloaded a chapter 3 save from a previous playthrough in an area where pop in was quite bad and it has been greatly reduced.

I also recommend you to turn on AllowSharpen - it also can't be changed in configurator, but makes picture better while not affecting fps at all (but it makes picture better only if you play at max resolution)
P.S. UberSampling=4 -> new benchmark for monster PC :D