| From initial viewing, they are nice, but in a lot of real world applications, they are not as nice as you would think. First off, a simple misconception is that 120Hz is what you are seeing, that's not really true; what you are seeing is the "Motion Enhancer" or whatever the respective companies want to call it, which is essentially frame interpolation. The TV does a pretty good job at guessing what goes inbetween the missing frames to make up for the jerkiness.
There are a couple problems with this. First, the TV doesn't always do a good job. When it doesn't do a good job you start seeing artifacts in the motion, stuff that definitely shouldn't be there. It'll look like pieces of the previous frame were left behind because it didn't guess right. Second, for movies, the "smooth" look makes it look unnatural. What I mean by this is, films were shot at 24 frames per second, so some camera jutter in panning is inherent, so when you take away that stutter, it starts to look like home video instead of a film. Obviously, some people may prefer that, but when it comes down to it, initially it will "Wow" people, but after the initial impression, people start to see it's not as great as they think it would be.
Now, 120Hz is just the refresh rate they chose to evenly get multiples of both 60fps and 24fps. So it is slightly faster than normal, so it still will make a slight improvement in motion resolve. I say slight because one you turn off the "Motion Enhancers" the motion starts to look a lot closer to your typical 60Hz TV's. The only difference is now with 24fps content (theatrical movies) looking as it should without having to do any 3:2 frame pulldown. The 3:2 pulldown judder is we've had ever since DVD's hit the market so many people will even think going from the 3:2 judder to a 24fps judder looks weird, even though 24fps judder is how it is supposed to be. | 
