Comment 74 for bug 138691

You are correct about the Samba shares. One case it applies to is in wireless network mounted drives that are mounted using wpa_supplicant. There is an ordering problem in /etc/init.d in that S15wpa-ifupdown is executed before any of the S??umount* scripts. This causes Samba to hang due to multiple network timeouts.

A workaround is to rename S31umountnfs.sh to S10umountnfs.sh in /etc/rc6.d. This forces network mounted drives to be unmounted before shutting down wireless. There are probably other ordering problems, but this fixes the network drive over wireless problem for me and shuts down much faster.