I visit a lot of websites. Often sites ask you to register so you can get special member only features or freebies or coupons. I used to frustrate myself by registering but then forgetting which email address I used to sign up, my user name, or password when I went back later.
To keep track I write down the info on a 4x6 index card. I file them alphabetically (by site) in an index card box. Now when I go back to a site and need to know my user name or password I just look it up quick instead of having to request the information by email. I also jot down any other info that might be helpful for that particular site (birthdays I used, security questions & answers, etc.).
Another tip is to have the same password for all these sites. Now I am not talking about your online banking accounts here! I am talking about sites like BettyCrocker.com or sites that don't include important personal information. Pick one password and stick with it...that way you'll always know your password. Most sites require at least one number in your password so throw in a number for good measure. :)
Sometimes your user name is your email address so if you plan on signing up at several sites create an email address just for that purpose. Having a junk email address keeps your regular inbox from being filled up with a bunch of special offers and ads.
I think I have mentioned this already to but just in case, I also don't use our real birthdates when filling out those forms. I just add one to the month and date and leave the year the same. It is to the point now that I am starting to think my birthday really is June 26th!
My hubby even has a few cards in the box. We keep it in the cupboard right next to the computer so it is easily accessible.