Everyone wants one, of course, but they are stupid.  From (one of) the "horse's mouth":

http://www.amazon.com/gp/product/B00BSREPRS/ref=as_li_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B00BSREPRS&linkCode=as2&tag=httpwwwchanco-20

How close to the TV must I sit to appreciate 4K?
The short answer is that between 5 and 6 ft. is the ideal viewing distance for a 55” or 65” Sony 4K Ultra HD TV.

However, on a 55“, you can now sit as close as 3.6 ft and enjoy a visibly smoother and more detailed picture (e.g you won’t see the individual pixels). On a 65“ TV, you can sit as close as 4.2 ft. to appreciate 4K.

Since the pixels on a 4K Ultra HD TV are four times smaller than on an HDTV, it becomes harder to see them. In fact, you can sit closer to a 65” Sony 4K Ultra HDTV than you can to a 35” HDTV. When you sit closer to the screen, you feel like you are immersed in the action. You get the same visual impact as you would sitting in the best seat at a movie theater.

I'm 6-feet tall, and I do not sit a "body length" from my TV; more like 12 to 18 feet.

Yet another absurdity of the capitalistic mindset, buying that which you do not need!  Regardless of whether or not you believe in global warming or not, a 4K TV will consume more energy than a standard HD set, which means that you'll be paying more for an appliance which is using more electricity (which comes, mostly, from a coal-fired plant.)

It does seem like home electronics are getting a bit ridiculous.  Always something new the manufacturers want people to buy.  Our "tv" is 17 yo, analog, gets no reception, but we can watch dvds