For some reason, all applications are no longer able to store credentials in the login keychain. This applies to Mail, Echofon (twitter), iDisk/MobileMe.
I have run Keychain Access and created a new keychain, so I now have an empty login keychain. The keychain is unlocked. However, when I log in to an application, it does not create an entry in the keychain, and will prompt for password again next time I start the application.
I have run Keychain Access, Repair to no effect. I have run Disk Utility, Verify Disk and Repair Permissions to no effect.
Any pointers appreciated.