Saw the 4k demo in Japan last October.It's amazing.
3-D gives me a headache.
Spot on Jp.
Saw NHKs demo of 'Super Hi-Vision' in 2009- left me gobsmacked at how good it was. Saw some of the Olympic footage they were doing in London- again incredible. Saw some 3D on the same (large) screen, interesting but still a novelty.
At the moment there's another big problem with 3D- the need for glasses. Example- my friend invited people round to watch a 3D event (can't remember which) but had to add that if enough people came they'd have to watch in 2D. That group vowing experience is great for big events (done it a number of times with F1) - with HD everyone there gets the benefit of the better picture. With 3D that's much more difficult, especially with viewing angles.