Is the scene camera looking at <0,0,0>? The best way to check is to position an object there and make sure the camera can see it. If you still don't see the cube, there could be another problem.
Check you don't have any script compilation errors. If this code was added since the last successful compile, it won't be included in the current wizard you see.
Note that this includes ALL compiling issues in your project, not just the script containing this code. If there are any compilation errors at all, Unity will revert to the last successful code compile.
That's about the only thing I can see possibly wrong with this right now, and I point it out as it has happened to me a couple of times before.
Make sure you didn't accidentally "un-render" the mesh for the missing object. It may sound obvious, but you never know. That would be something I'd do by accident. lol.