I have found that it is best to keep a hard copy of my e-mail address book and user names and passwords, just in case of computer loss or my memory failure. I use a 3 by 5 inch spiral notecard book. At the front, I have my information for my personal email accounts. Then I mark pages through the alphabet with 2 or 3 pages for each letter. On these, I record my friends' and family's names and emails. I also record the sites I go to and my user name and password for each site. Towards the back, I have my information for all the bills I pay on-line.
This has been a real help to me in the past when I had a computer crash or changed computers. I take my notebook with me if I need to go to the library to use one of their computers.