Thanks for the array of responses. I was particularly impressed with an idea davido had. We could each select a keyword / phrase then that pair (login + keyword for example) could be made accessible only by the gods.
Voila! Instant keyword/phrase implementation of your idea, without someone having to code it up. If you forget your DigitalKitty login, just login under your second account and ask someone to change the DigitalKitty password. When they challenge you, point them to your homenode.
Backup passwords/accounts tend to be worse than useless, because if you're going to forget your primary password, you'll forget your backup as well because it is used even less.
davido's suggestion adds a layer of complexity while still being vulnerable to the original problem. And if your solution to the forgetting problem is to make the keyword your mother's name, or your favourite band, you might as well just use that as your password.