Make the top panel appear at mouse-hover event

I really don't like that the top panel is static; it wastes a lot of space on the screen and most of the time it is inactive. I'd like an option to be added to make the top bar spawn at mouse-hover event, with the applications maximized at full screen (i.e. up to the top borders of the screen). No matter if this won't be the default behaviour, but it would be fine to give users the chance to change that (just like in Mac OS X). In Mac OS X the static top bar is motivated by the fact that it is used to show the global menu (like in Ubuntu with Unity).

I don't think that's a problem to implement that.