I'm resurrecting this thread, because I'm having the same issues now.
Basically, I cannot unlock my keychain, be it to get passwords out or put passwords in. This is a particular problem, because I cannot set my .mac password in the Internet control panel, and I want to try the iSync bookmarks thing, but it's also proving to be a nuisance with my other e-mail accounts.
It should be noted that it's not just that my password isn't working to unlock the Keychain, because I'm not even being asked for my password. I've found no error messages in the Console, and no dialogs are put up on screen. Even going into Keychain Access and attempting to unlock my Keychain there is not helping (clicking the Unlock button does nothing).
Disk First Aid seems to be checking out OK, and repairing permissions didn't help. Anyone else have any ideas as to what I might be able to do here?