Comment 3 for bug 439604

Thank you for taking the time to report this bug and help to improve Ubuntu.

Effectively, this is by design; filesystems that aren't required to bring up the desktop should not block the desktop, they should be handled in parallel. However, there's probably a use case for users being able to configure mountall (which is what handles fscks and tells gdm when it's ok to start) to be more strict in waiting for additional filesystems to start up, as well as for mountall feeding progress information via usplash; so reassigning this to the mountall package for Scott to weigh in.

As a workaround, I believe you could change /etc/init/gdm.conf from
  start on (filesystem and ...
to
  start on (stopped mountall EXIT_STATUS=0 and ...

to declare that you don't want gdm to start up until all your drives are mounted. This is not something that should be set as a default in the distribution, however, since it would have adverse interactions for any users who automount network filesystems at boot time.