We need linux-headers-* to install dkms. Without it, we get the error:

Stopping VirtualBox kernel modules ...done.
Uninstalling old VirtualBox DKMS kernel modules ...done.
Trying to register the VirtualBox kernel modules using DKMSError! Your kernel headers for kernel 3.2.0-54-virtual cannot be found.
Please install the linux-headers-3.2.0-54-virtual package,
or use the --kernelsourcedir option to tell DKMS where it's located
 ...failed!
  (Failed, trying without DKMS)
Recompiling VirtualBox kernel modules ...failed!
  (Look at /var/log/vbox-install.log to find out what went wrong)