If you have installed Ubuntu Intrepid as a virtual machine in your Virtualbox, you will find that the mouse integration does not work, even after you have installed the guest addition.
If you are having this problem, here’s the fix:
First, make sure that the guest addition is already installed inn your Ubuntu Intrepid guest.
Open a terminal, type
gksu gedit /etc/X11/xorg.conf
Add the following lines to the end of the file. Save and close
Identifier “Configured Mouse”
Restart the computer. The mouse integration should work now.