Pretty simple plugin to hide the statusbar in Calibre.
Personally I think it gives the interface a cleaner look, and I generally don't need the information shown there.
This plugin still allows the status bar to be shown with either a button or keyboard shortcut Ctrl+Shift+S.
Download this repository as a zip file and import it into Calibre:
Settings -> Advanced -> Plugins -> Load Plugin from file
Calibre will need to be restarted for plugin to take effect.