It's unlikely you have a screen that will actually display this video from Jake Scwharz at its full 4K resolution — that's four times 1080p — buuut you might have a screen that's better than 1080p at least (a fancy 27-inch iMac, for instance), which can give you a taste of why, if anything, 4K is the next major thing in teevee.
There is a certain kind of brutal inevitability to 4K or ultra-high-definition displays: It constantly gets cheaper to manufacture displays that are more pixel-dense than the year before. (If you buy a new phone this year that isn't an iPhone, it'll be 720p or 1080p, mostly likely.) So it's a fairly straightforward path for where TVs go next: one lined with more pixels. And while the leap to 4K won't be quite as staggering as the one from standard definition to high definition, the case for it is much easier to make than 3-D, particularly once the prices of ultra HD displays fall to relatively affordable levels.
Oh, and make sure you click on the little gear in the YouTube window and switch it to the "Original" resolution to see it at 4K. (via)