This article cuts the hype:
http://www.theregister.co.uk/2013/06..._eyes_have_it/
An important message is that if you want any real benefit from 4K or 8K then you need a higher frame rate. Still pictures can use the full resolution but as soon as anything moves you lose a lot.
I saw a demo of NHK ultra high resolution TV during the Olympics. Not sure whether the screening was in 4K or 8K nor do I know the frame rate but it was impressive. On a big screen with wide angle shots you could see all the detail. It was like sitting in one of the best seats in the stadium.