My TV is old and busted (new hotness coming in a couple months), so it doesn't support any motion smoothing. However, I do have a software program on my PC that can do it. The plus side is that it has two different settings: the first is to double the framerate (so most videos will play at 48fps) and then where it will match whatever my monitor's refresh rate is (60fps in this case, it's a IPS monitor).
I was surprised to find that I could see a clear difference between them. By direct comparison, 48fps looked more natural. Kind of like the difference between 24fps and 30fps, except, you know... double.
Anyway, the sad thing is that my new TV probably won't have a direct 48fps option, it will simply take it up to whatever (I believe it's only 60fps, despite the whole "120Hz" thing). Most movies do look a bit odd that way, so I think in general I'll be sticking to "original" framerate. If it was shot normal 24fps, I'll stick with that.. if it was shot HFR, then I'll stick with that.
To be honest, The Hobbit actually looks "off" to me in 24fps.