Check out LastPass. It's more secure than paper, and more convenient. The problem with paper is:

1) you won't change passwords and won't make them unique for each site
2) You won't make them complex and long
3) It won't be with you when you need it. (You can carry an app in your smart phone, but that metal box is a PITA)
4) You'll leave it unlocked and that piece of paper will sit around unsecured on your desk, table, counter etc.