Weird. I checked in on my cube today and found the fuse all melted, still worked though. Then this thread shows up in my "Show new replies to your posts."
I had the same thing happen to my cube, was working fine, came back a couple of hours later and the fuse was smoked, cooked the main board pads. I had to solder an external wired fuse holder in to get it working (it actually cooked holes through the fiberglass main board).
I doubt it is caused by an over supply, that should just blow the fuse. In my case I suspect a faulty connection that caused the fuse holder to over heat.
I too blew [aka melted] a fuse on a unit which had been running perfectly for 3 months. I had disassembled it to take the new HD pictures and put it back together. The fuse melted within a few hours, but the unit was absolutely fine with a replacement. Could have been static, could have been bad placement of the fuse (doubtful), who knows. What we do know is the fuse is pretty close to the max power of the fuse.
Its also nothing to do with fans, the Cube has PWM detection and will stop hashing if the fan fails. You can test this yourself (please dont).