Gregory's Server@CatDragon a good password is one that is hard to crack, is unique to the account (so if it is leaked then it only affects one account), can be secret, and can be changed when needed.
Fingerprints are great for identification, though - they could probably replace usernames.
@mikeburns I change all mine every week or so and am enough a Luddite to keep them in a notebook rather than stored online.