This isn't the sort of invisibility or disappearance where you can see right through something. Instead, it's more like turning the contrast on something down so far that all you can see is (for lack of a better term) a black hole where the thing used to be. This is taking advantage of the fact that carbon nanotubes can be engineered into standing, nanoscopic "forests" that light can't find its way out of, meaning that whatever light falls onto something never gets reflected back out to your eye. NASA uses this stuff to blacken the inside of telescopes, but a group of researchers from the University of Michigan has started trying to conceal objects with it.
The pic does a pretty good job of showing how this stuff works: it takes any sort of reflection that would give your eye a chance to discern the shape of an object and turns it completely flat black. So, if you were to paint something with this stuff, it would effectively render it two dimensional, like a black paper cut-out. No matter how you were looking at it, you'd never be able to see anything that would suggest depth, which would be quite effective, at least at night.
As far as I can tell, the only real problem with this stuff is that you're going to be hard-pressed to find a black enough background to blend into. So instead of turning invisible, it'll be more like, "hey, look at that tank-shaped void over there!"
Images courtesy the American Institute of Physics.