looks, like your /opt got somehow unmounted.
what says

mount

?

so what does it mean ?what can i do ?

just execute the command

mount

like you did with the others. it should list the mounted filesystems, hopefully giving a hint, why /opt disappeared.

tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev,noatime,size=65536k)
/dev/mmcblk0p2 on /home type ext3 (rw,noatime,errors=continue,commit=1,data=writebac k)
/home/opt on /opt type none (bind)
nodev on /sys/kernel/debug type debugfs (0)
/opt/pymaemo/usr/lib/python2.5 on /usr/lib/python2.5 type bind (bind)
/opt/pymaemo/usr/share/pyshared on /usr/share/pyshared type bind (bind)
/opt/pymaemo/usr/lib/pyshared on /usr/lib/pyshared type bind (bind)
/opt/pymaemo/usr/share/python-support on /usr/share/python-support type bind (bind)
/opt/pymaemo/usr/lib/python-support on /usr/lib/python-support type bind (bind)
/dev/mmcblk0p1 on /home/user/MyDocs type vfat (rw,noauto,nodev,noexec,nosuid,noatime,nodiratime, utf8,uid=29999,shortname=mixed,dmask=000,fmask=013 3,rodir)
/home/user #

hm, interesting.
/opt is still mounted.
the output of

ls -al /opt/

and

ls -al /opt/var/

and

df -h

please.

home/user # ls -al /opt/
drwxr-xr-x 9 root root 4096 Sep 24 09:39 .
drwxr-xr-x 24 root root 1568 Jan 2 2009 ..
drwxr-xr-x 2 root root 4096 May 12 00:22 lib
drwxrwxr-x 3 root root 4096 Sep 23 00:21 maemo
drwxr-xr-x 3 root root 4096 Sep 24 09:39 mirror
drwxrwxr-x 4 root root 4096 Sep 24 05:19 mobilehotspot
drwxr-xr-x 3 root root 4096 Sep 24 05:19 pymaemo
drwxr-xr-x 6 root root 4096 Jan 2 2009 usr
drwxr-xr-x 4 root root 4096 Jan 2 2009 var
/home/user # ls -al /opt/var/
drwxr-xr-x 4 root root 4096 Jan 2 2009 .
drwxr-xr-x 9 root root 4096 Sep 24 09:39 ..
drwxr-xr-x 3 root root 4096 Jan 2 2009 cache
drwxr-xr-x 3 root root 4096 Jan 2 2009 lib
/home/user # df -h
Filesystem Size Used Available Use% Mounted on
rootfs 227.9M 137.2M 86.5M 61% /
ubi0:rootfs 227.9M 137.2M 86.5M 61% /
tmpfs 1.0M 96.0k 928.0k 9% /tmp
tmpfs 256.0k 92.0k 164.0k 36% /var/run
none 10.0M 72.0k 9.9M 1% /dev
tmpfs 64.0M 4.0k 64.0M 0% /dev/shm
/dev/mmcblk0p2 2.0G 148.9M 1.7G 8% /home
/home/opt 2.0G 148.9M 1.7G 8% /opt
/opt/pymaemo/usr/lib/python2.5
2.0G 148.9M 1.7G 8% /usr/lib/python2.5
/opt/pymaemo/usr/share/pyshared
2.0G 148.9M 1.7G 8% /usr/share/pyshared
/opt/pymaemo/usr/lib/pyshared
2.0G 148.9M 1.7G 8% /usr/lib/pyshared
/opt/pymaemo/usr/share/python-support
2.0G 148.9M 1.7G 8% /usr/share/python-support
/opt/pymaemo/usr/lib/python-support
2.0G 148.9M 1.7G 8% /usr/lib/python-support
/dev/mmcblk0p1 27.0G 1.6G 25.4G 6% /home/user/MyDocs
/home/user #

odd. output of

ls -alR /opt/var/cache/

home/user # ls -alR /opt/var/cache/
/opt/var/cache/:
/home/user #

very odd.
try to recreate the necessary directories:

mkdir -p /opt/var/cache/apt/archives/partial/

if that went without any message, check with

ls -al /opt/var/cache/apt/archives/

that should list partial
then try

apt-get update

to recreate the package caches.

ome/user # mkdir -p /opt/var/cache/apt/archives/partial/
mkdir: cannot create directory '/opt/var/cache/apt/': Input/output error
/home/user # ls -al /opt/var/cache/apt/archives/
ls: /opt/var/cache/apt/archives/: No such file or directory
/home/user #