Saw the film in IMAX, 3D and 48FPS.
The first five minutes of 48FPS felt strange, but after a few minutes you adjust. I really liked it. Everything felt incredibly realistic, and with the 3D it sometimes felt like you were there. By far the most immersive theater experience I've had.
I will say that the use of 48FPS will make filmmakers adjust their style. Peter Jackson seems to have a bit. One of the reasons Michael Bay can have his shakycam on steroids thing is because the motion blur basically hides much of the actual motion; if you were to do shots like that at 48FPS you'd throw up. Some shots in the Hobbit where the camera was moving quickly made it look like things were moving too quickly, but these were only a handful. Overall I was impressed. Once you get over that shock it really works; at first it seems like everything is moving fast, like when you fast-forward a movie, but it's really just because you see every movement, every wrinkle of fabric or crumpling of paper when people are doing things, when your brain accepts that after a minute or two there isn't any problem. And it works really well with the 3D--I can't imagine shooting one without the other. I hope more movies do it this well. The 3D alone rivals the best examples I have seen. 48FPS just was the icing on the cake. After a while you don't notice it--reminds me of watching widescreen on 4x3 TVs in the 1990s, you just sort of forget about it after a minute or two--but if the movie were to suddenly shift to 24FPS halfway through you would think it was all blurry and slow.