I configured Virtualbox guest machine to run Ubuntu 13.04 (Raring Ringtail) but performance is just not acceptable. It probably has to do with my host machine not having a good enough graphics hardware.
Anyway, to make it bearable, I have gone Gnome Fallback mode.
Anyway, below is my clean configuration from scratch to have a better performance running under VirtualBox.
Initial clean-up and pre-requisites, open terminal (Ctrl+Alt+T):
Log out from session
From the GDM, select Gnome Fallback(No effects), see below for screen capture.
Log back in to Ubuntu. To make it even better, install VirtualBox guest additions. But first let us install the pre-requisites and some clean-up.
From VirtualBox Guest main UI, select Devices | Install Guest Additions....Hit on cancel for the window like below.
Of course you have to change folder location (with your username) and version based on your VirtualBox. After reboot, you have pretty good setup for daily use.
This applies to 13.10, 14.04, 14.10.