I frequently use Linux in VirtualBox as a testing and hacking environment. It got really annoying when I would go to the Gnome menu bar and the OSX Menu bar would pop up overtop of the Gnome menu bar!
Luckily, the guys (or gals) over at Eternal Storms Software have an awesome app called PresentYourApps. Once you’ve installed it, set VirtualBox VM to “Remove Menu Bar and Dock”
Then, restart VirtualBox — no more Menu Bar!