I saw it in both HFR and non-HFR, both 3D and both at Imax, and I thought the HFR was a million times better for action, though in the very first opening sequence with Bilbo's hobbit hole it looked super cheap/fake at first. But the action shots (especially the combats, they were INSANE), the eye NEEDS those extra frames to catch all the motion. You just can't process that much data, you need the extra frame rate to follow all the cool moves and counter moves the dwarves do. From the dishwashing songs, to the outdoor panning shots with the wargs, to the goblin orgy of violence and bodies bashed about, I thought that HFR gave me literally double the action. I will never buy in in 24p, and I use frame interpolation all the time on my movies from my HTPC, even though my PC can only handle 720p for now (1080p is often too high...though it depends on the bitrate).
Watching The Avengers in 60fps was SO good using SVP, though there are still some minor shimmering artifacts visible in other shows, it really depends on the rez and bitrate. Once I can get 1080p video up-converted from 24p->60p in realtime, next step is 48hz in3D. I am one of those crazy guys who'd probably even upscale 48p to 60p while I'm at it. It'll be processed, sure, but just that much more snippy. Now if only my projector could accept 144hz so I could double flash 72p rather than triple flash 24p, that would be super cool. I remember setting my mouse refresh to my CRT's refresh, like 72->85hz back in the day, and it is so much smoother. Just move the mouse around and you see/feel the difference immediately. 60hz is still too low, we need 72hz or even 120hz per eye. But in Blurays, I get why he did 48hz, since movie projectors often double flash 24hz to 48 anyway, but I wish they'd designed 3D Blurays to support up to 60hz per eye. Maybe it's just a question of encoding? I don't see why, other than the space required, you couldn't have a 60p 3D 1080p Bluray disc, even if you need two for a movie like The Hobbit. I'd rather buy a movie that uses two discs, old school style like the DVDs of LOTR, than 1/2 the frames.
Of course, then the problem becomes, my projector doesn't accept more than 1080p/30, but that's another issue I can solve with another upgrade.