This option helps to hide by default the VMware top bar in full-screen view.
The purpose is to get almost all of the VMWare Player UI
out of the way so you can focus entirely on the guest OS.
For auto-hiding the bar in in full-screen mode use:
pref.vmplayer.fullscreen.autohide = "TRUE"
To shrink the size of the hidden toolbar, specify zero pixels.
VirtualBox has full support for the disk formats of VDI, VHD and even VMware's
You can share the disk, but not the virtual machine itself.
You will need to create two virtual machines, one for each virtualization product,
but you may share the disk in VMDK format.