If you use Virtual Box for virtual machines (eg testing web sites in IE, what fun) then this is of interest to you. There is another feature which I have only just discovered called Guest Additions.
This is something that you can install into your VM which gives much tighter integration with the host OS. For example no more having to capture/uncapture the mouse and full copy and paste compatability. Its incredibly easy to use once its installed.
To install Guest Additions, just fire up the VM and then go to the Devices menu at the top. At the bottom of this menu is the option Install Guest Additions.
That’s it, very easy, highly recommended