The really sad mistake is to
1) Be paranoid about using your normal email address when signing up to anything
2) Work for a firm that censors webmail providers such as hotmal, yahoo...
3) Make up a random email address
and finally, after leaving yourself logged on for a week and then rebooting
4) Find you have forgotten what that address was
This happened to a friend of mine; I think it was one of the very first games I played - it certainly gave me my first timeout
As you can see, I made the opposite mistake of not obfuscating my user name at all. Ho hum.