I got a new laptop recently, then changed my login password shortly after installing Ubuntu. The Gnome keyring manager was still using the old password, so every time I restarted the machine, I was prompted for the keyring password. It isn't obvious how to change this. I did quite a bit of googling and found a lot of questions about it, but no solution that works for Ubuntu 10.04 with Gnome.
Here is the answer:
1. Log in as usual. Enter your old password in the keyring manager when it asks you to.
2. On the main Ubuntu menu, go to Accessories, Passwords and Encryption Keys.
3. On the Passwords tab, right click on "Passwords: login". This was the non-obvious part.
4. Choose "Change Password". Fill in your old password and your new password.
It looks like how this has been done has gone through a lot of changes over the past couple of years, so these instructions will likely be out of date when 10.10 comes out.