I saw it in IMAX 3D @48fps yesterday evening. I enjoyed the movie a lot, and the 48fps didn't bother me much after the first few minutes. It made 3D seem much better, I think.
My only problem was what it did to the light in the movie. Although in soft light areas, it seemed a lot more realistic, in brighter areas (like the sun on the landscape or the braziers in Goblin Town for example), the light seem too harsh. Especially since I was expecting a digitally graded movie like LotR was to offer perfect coloring. It also made a few special effects seem a bit fake.
The first is probably an editing and a filming issue. With better lenses, filters, and adjustments to lighting conditions it will help, and with better adjustments of the color values in editing it can be fixed. The second will get better as digital technology improves.
I'm going to go see it @24fps this weekend if I can to compare.