Once in a while I have had the problem that I tried to change the password on a website, but for some reason it wasn't correctly saved there. But the new password was already stored in the keychain. I then have to fix that with the "I've forgottten my password" process.
On Windows I use Password Safe, which has password history. You can set it to save a X number of passwords.
The benefit of having a history is also that you can look back to when passwords were changed.
So, supporting password history (with date/time) would be a nice addition.
