Hi,
as non-root user I mounted the same windows share at the same mount point more
than once (see sequece bellow) 
Next I was trying smbumount to the last mount: those has been unmounted.
Previsous mount I found in this mount point, but it is invisible in system by
`df -a` or `mount` tools.
Gentoo, kernel 2.6.12, samba 3.0.14a

vv@bubak ~ $ smbmount //server/vv /home/vv/smbshare -o username=vv
Password:
vv@bubak ~ $ smbmount //server/vv /home/vv/smbshare -o username=vv
Password:

vv@bubak ~ $ df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/hda1             10000072   2847724   7152348  29% /
udev                    258172       148    258024   1% /dev
/dev/hda6              1999932    499376   1500556  25% /var
/dev/hda7             65149556  14018708  51130848  22% /home
none                    258172         0    258172   0% /dev/shm
//server/vv            222797824  99430400 123367424  45% /home/vv/smbshare
//server/vv            222797824  99430400 123367424  45% /home/vv/smbshare

vv@bubak ~ $ mount
/dev/hda1 on / type reiserfs (rw,noatime)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)
udev on /dev type tmpfs (rw,nosuid)
devpts on /dev/pts type devpts (rw)
/dev/hda6 on /var type reiserfs (rw,noatime,notail)
/dev/hda7 on /home type reiserfs (rw,noatime)
none on /dev/shm type tmpfs (rw)
usbfs on /proc/bus/usb type usbfs (rw,devmode=0664,devgid=85)
binfmt_misc on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)
//server/vv on /home/vv/smbshare type smbfs (0)
//server/vv on /home/vv/smbshare type smbfs (0)

vv@bubak ~ $ smbumount /home/vv/smbshare
vv@bubak ~ $ df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/hda1             10000072   2847724   7152348  29% /
udev                    258172       148    258024   1% /dev
/dev/hda6              1999932    499376   1500556  25% /var
/dev/hda7             65149556  14018708  51130848  22% /home
none                    258172         0    258172   0% /dev/shm

vv@bubak ~ $ mount
/dev/hda1 on / type reiserfs (rw,noatime)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)
udev on /dev type tmpfs (rw,nosuid)
devpts on /dev/pts type devpts (rw)
/dev/hda6 on /var type reiserfs (rw,noatime,notail)
/dev/hda7 on /home type reiserfs (rw,noatime)
none on /dev/shm type tmpfs (rw)
usbfs on /proc/bus/usb type usbfs (rw,devmode=0664,devgid=85)
binfmt_misc on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)