Gnome 3 has a wonderful UI, but one glaring fault. The top system bar serves as a "title bar" for your current application, telling you what app you have open, and allowing you to exit the application from the bar itself. Unfortunately, the default theme, Adwaita, has huge looking titlebars, which don't really get in the way when you are working in normal sized windows. When the windows are maximized though, you have 2 titlebars taking up precious screen realestate: the big Adwaita titlebar, and the system bar up top.

Fortunately its real easy to fix this.

Open your Adwaita xml (/usr/share/themes/Adwaita/metacity-1/metacity-theme-3.xml) file and change the line that configures the maximized window (name="max"). Add has_title="false" to the "frame_geometry" tag. Then look for "title_vertical_pad", and change "value=9" to value="1". Restart Gnome 3 and maximize a window. *poof* the UI makes sense now.

Interestingly, you can still drag down from a menu or button bar to return to a normal sized window and get your duplicate titlebar back.