Indeed, I have one also. I thought about solving it for a couple
of months now. Never wrote anything down, I think I just have a
working knowledge of the types of transforms needed. It took me
about 1.5 hours to solve it. I thought I had ALL the necessary
tools, but there is still one tool that alludes me. It happens
half the time, and when I get it, I try to mess it up just enough
to allow it to be solved again. As ACW pointed out, most
intuition about edges and centers is WRONG. The first thing I
tried to the original solved cube was the extended Pons. Much to
my dismay, it didn't work. So if you think you know how to
extend your 3x3x3 transforms to the 4x4x4, put your fingers where
your mouth is!!