also experienced the shutdown-problem "occasionally", using fstab, on both Edgy and Feisty, both x86 and PPC, with KDE 3.5.6 - not anymore on 3.5.7 it seems until now.
On a sidenote, I am currently struggling with a "Permission denied"-problem on a new share although all other shares are configured the same way and work fine (?!):
Cannot even "touch" a file as superuser (?!).
Here is my fstab (I tried both "gid=100" (for users-group access) and "1000" to no avail):
Currently I am stuck and would consider nfs if there were only Linux-clients in my network... (is it much overhead to run a NFS-server alongside Samba?)
//jagor/grexdox /media/grexdox cifs exec,credentials=/home/grexe/.smbcredentials,iocharset=utf8,uid=1000,gid=1000 0 0
//jagor/backup /media/backup cifs credentials=/home/grexe/.smbcredentials,iocharset=utf8,uid=1000,gid=100 0 0