To make a backup of the saved passwords in Ubuntu just make a backup of the folder
~/.gnome2/keyrings/. This is where Gnome stores its password keyrings (named something like
You can also export all your passwords from the Gnome Keyring using the python module keyring as described in this blog post by Michael Susens-Schurter. (A backup of his script can be found on https://gist.github.com/947237).