Re: 60Hz vs. 120Hz vs. 240Hz TVs
People like to buy things with more and bigger numbers associated with them, even if they have no idea what it means.
A Hz is unit of frequency, 1Hz being equivalent to 1 interval a second. 2Hz being 2 intervals per second. You can equate this to the maximum number of changes to an image in a second ie: your frame rate cannot physically exceed the refresh rate. Any frames higher than the refresh rate are effectively dropped, and you never see them.
In general more Hz are better, but it isn't cut and dry. Smaller viewing areas require more Hz to look fluid than larger viewing areas, the same goes for being closer to a viewing area than further away. The limiting factor is.. you.
A human can only detect a limited upper boundary of motion (the average is somewhere around 60hz). That being said, the larger the viewing area, the more data for us to process at once, means that it takes more time for us to recognize what is going on. In those cases (such as movie theaters) 24hz is fine. At home sitting in front of a computer playing a video game on a 19" screen, is less area to take in and requires more hz (typically 60). TVs being in the middle ground, should only require something between the two.
To add to the mess, standard hdtv resolutions don't support more than 60hz. TVs running at higher than 60hz are either displaying a frame more than once, or fiddling with the frames. Note that most movies are not recorded onto disc at 60fps, check the back of your dvds for the format, you can look it up online. Most are at 24hz and upscaled.
Then comes 3d. The basic rule is that if at 60hz is fine for 2d, then you need to double it for 3d.