I went from getting 35-50 FPS with everything on low to getting 55-70 FPS with Normal graphics and Standard anti-aliasing. I don't see any FPS drop between low and standard anti-aliasing now (I might change it back to low because a couple people were saying that anti-aliasing adds a bit of input lag in more graphically intensive areas like the larger towns, but I haven't tested it enough myself to confirm). I get 80+ FPS with the graphics on low, but the view distance is so much further on Normal that the 10-20 frame loss is worth it for me right now until they make view-distance it's own setting.

I'm not a "pro gamer" so I didn't really notice an input lag before, but the game does just feel way smoother now and there's no jittering or stuttering at all.

I'm not sure what's causing the alt-tabbing problems for other people; I'm not having that issue at all. The game takes 2-3 seconds to tab in and out of it for me and I haven't had it crash from tabbing at all (yet).