Comment 2 for bug 367782

This was plaguing me too until I found the above post. For me, the steps to reproduce are:
1) Enter the drive to be mounted in /etc/fstab -- something like:
    UUID=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX /mnt/backup ext3 defaults,relatime 0 0
2) sudo mount -a -- which would succeed
3) sudo reboot
4) Login
5) mount

At this point, I expected to see the drive properly mounted like:
   /dev/sdc1 on /mnt/backup type ext3 (rw,relatime)

However, it was not mounted. In the dmesg log - I would see where the other drives got mounted, and that it recognized the usb drive as sdc.

The crazy thing, is that if I did a shutdown -P 0 and powered off completely, all drives would mount properly on power up from a cold start.

As a workaround, I too have added the "sleep 10" line to the /usr/share/initramfs-tools/init file and then sudo /usr/sbin/update-initramfs -uk all to rebuild the image.

FYI - this is on 9.04