I don't have more than one device mounted to the same directory. I just have my external hard drive always being displayed in a Nautilus application window on start up.

Did you try to install Hardy Heron Beta yet instead of just running the live CD.  If you have a separate /home partition from your root partition as I do, then if you choose you could always put Feisty back     on without losing any personal data.  I when back in forth a few times with nor data loss.  I didn't even loose my bookmarks in Firefox.

Hardy has had almost daily software updates, so it is getting fairly stable.

Your troubles may go away with a install as opposed to a live CD run.

Below is my mount data; /dev/sdb1 always comes up in Nautilus on startup, a USB external drive.
dave@dave-laptop:~$ mount
/dev/sda3 on / type ext3 (rw,errors=remount-ro)
proc on /proc type proc (rw,noexec,nosuid,nodev)
/sys on /sys type sysfs (rw,noexec,nosuid,nodev)
varrun on /var/run type tmpfs (rw,noexec,nosuid,nodev,mode=0755)
varlock on /var/lock type tmpfs (rw,noexec,nosuid,nodev,mode=1777)
udev on /dev type tmpfs (rw,mode=0755)
devshm on /dev/shm type tmpfs (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620)
lrm on /lib/modules/2.6.24-12-generic/volatile type tmpfs (rw)
/dev/sda2 on /home type ext3 (rw)
/dev/sda1 on /windows type fuseblk (rw,nosuid,nodev,noatime,allow_other,default_permissions,blksize=4096)
securityfs on /sys/kernel/security type securityfs (rw)
/dev/sdb1 on /media/40GB type vfat (rw,nosuid,nodev,uhelper=hal,shortname=mixed,uid=1000,utf8,umask=077,flush)