I am pretty good about jotting down my user name and password (and you need both) but somewhat less good about remembering where I put the piece of paper.
Sue and I nag each other about putting all passwords in an old organizer book that we keep in the office but still we miss some.
My Mac laptop has a built in program called keychains that encrypts usernames and passwords and stores them for any sites I access.
All I have to remember is the password to log into my laptop. I am sure that Windows machines offer a similar feature.