Ubuntu uses Centralized password management tool called Seahorse. This tool is a front end GUI to GNOME’s keyring management system. In simple this tool stores all passwords with a master password which is normally same as login password. This tool can manage your PGP keys, SSH Keys and pass phrases we use in different applications in Ubuntu.
You can find the Seahorse tool in Ubuntu main menu -> Applications -> Accessories -> Passwords and Encryption Keys.
In practical I face a problem once I change my login password. You can change password either through System -> Preference -> About me -> Change Password… or you can use shell command passwd. I use to change my password in either of these ways. In both the cases, I encounter Enter password to unlock your login keyring prompt dialog box during my first login after changing password.
SeaHorse uses your login password as master password to unlock its pass phrase storage box. When you change the password, it is NOT updated to SeaHorse (at least, this is what I believe). So the new login password fails to unlock Seahorse storage box.
The simple command line way to do it is to remove the ~/.gnome2/keyrings/login.keyring.
In GUI way:
Step-1: Ubuntu main menu -> Applications -> Accessories -> Passwords and Encryption Keys
Step-3: Enter your old login password and new login passwords.
You are done. Next time, it won’t ask for any login password for GNOME keyring. If Ubuntu integrate this change while changing the user password, it would be better user experience.