After installing the MarsEdit 1.2 update it asked me if I wanted to update the Keychain.
When I clicked Change All it began hitting the hard disk so hard it basically stalled the computer.
I had to Force Quit MarsEdit and other programs and restart.
Now I find that programs are asking for their login password, as if the Keychain file has been damaged in some way.
Also for some reason, Entourage refuses to complete its startup. I get the menu but the Inbox never appears.