i have a ubuntu10.10/win7 dual boot. i use win7 as a host for virtual box and run the existing ubuntu in virtual box.
when i installed vb additions and extensions, the xorg.conf file got overwritten.
depending on how i would boot (natively or through virtual machine) i have to change xorg.conf file manually. is there a way to make it automatic? putting both configs into xorg.conf file didn't work.
i filed a ticket couple days ago http://www.virtualbox.org/ticket/8360 but got no response. i'm sure there is a quick fix for this. any ideas??? i documented my experience (if u need more details) here: http://kirilligum.wordpress.com/2011/02/17/run-existing-linux-ubuntu-10-10-partition-in-virtualbox-under-host-windows-7-system-on-thinkpad-x201t/