Since I upgraded to VirtualBox 4.1.0 on my 11.04 I'm having a problem of suspending. This is a known bug and some suggested a workaround by adding the vboxdrv to the modules under /etc/pm/config.d/unload_modules. This indeed solved the problem but only when a VM image is not running.
Any clue how to workaround it until Oracle fixes the bug?
EDIT: Problem got solved in a future release of Virtualbox.