If you connect to your n900 using bluetooth a lot, you'll notice that there are restrictions on the folders that you can browse using bluetooth.
Luckily there is a very simple fix to add extra links to bluetooth browsing
if you run 'ls -al' you will notice a directory called .obex-root without write access for current user. Once you modify that folder to have write access, you can symlink any folder on your filesystem
chmod 750 .obex-root
(to symlink your memory card.)
ln -s /media/mmc1 Card