I can't recall where I saw a site navigation laid out in a cube but I thought it was unique when I first encountered it. What I didn't realize was the increased engagement the cube navigation led to. It was something new and interesting...I suspect that will be the case with other users too.
The author posts that this solution is for a "form that is too long", sometimes that is unavoidable (imagine a mortgage application). A cube based form could help user drop off by cueing the user to what was finished, what is next, and how much is remaining.
I've been playing with a similar interface that I think would be an interesting way to navigate through comments. It's best when viewed with an iOS device, since it supports touch control, but it works on a modern desktop web browser too by click-and-dragging:
The closest thing I can find that resembles it: http://www.paulrhayes.com/experiments/cube-3d/
The author posts that this solution is for a "form that is too long", sometimes that is unavoidable (imagine a mortgage application). A cube based form could help user drop off by cueing the user to what was finished, what is next, and how much is remaining.