I was using Ubuntu 12.04 with Gnome3 for a while, than started back on Unity.
My problem is that the super button only opens the Dash when there are already a few windows in a workspace. When the workspace is empty (there are no windows on that workspace), the only way to open the dash is clicking on the ubuntu icon in the launcher.
Is this the expected behavior or do I have some problem?
The problem was caused because I had turned off the Desktop handling by nautilus. So, it seems that this shortcut only runs when there's at least the nautilus Desktop or something else running on that workspace.
It looks like a buggy feature to me. I'll post a bug issue later on when I confirm how to reproduce it, and see what people from the dev team say about it.