GNOME Shell – How to Hide the Top Bar in Ubuntu

You can't currently autohide the panel in Unity. It is also not a planned feature.

There are ways you could possibly make the panel autohide:

• Post an idea on Ubuntu Brainstorm to add this option and hope a developer sees it and implements it or creates a for with this feature.
• Report a bug on Launchpad stating that this option should be available and hope a developer sees it and implements it or creates a for with this feature. This will probably get marked as opinion or invalid or at best a wishlist bug.
• Get the code and add this option then merge with trunk or create your own fork.

None of these are immediate or even likely.

There's a new extension available now which does the job: Location Icon Autohide.