I'm trying to keep an open mind on the topic... but I saw ARRI's test comparing 24 fps shooting and projection (of 2-perf 35mm material, digitally projected at CineGear) to 48 fps shooting and projection.
The look of 48 fps wasn't particularly appealing to me. Sure, there was a reduction in grain and an increase in smoothness, but it made everything look like it was shot on interlaced-scan video. I guess the 24 fps look is too ingrained in my mind to accept the look of 48 fps.
I'm becoming more convinced that I'd rather see 4K at 24 fps than 2K at 48 fps, as opposed to what James Cameron has proposed. Though I can understand intellectually that a fast-moving, fast-cut 3D action film should benefit from 48 fps... but my brain is telling me that it would make "Avatar 2" look even more like a video game and less like a movie.
But then, I'd also rather see 2D 15-perf 65mm IMAX than 3D 2K digital in terms of having an entertaining immersive experience.