If it's a site I don't care about and it doesn't let me log in via some form of OpenID or similar then I don't log in there. I have various sites with my real name or with this handle. I game (as much as I actually do) under another handle on both Steam and Origin.
For those who care, I'm Christopher E. Stith. My online handles and nicknames over the years include cestith (@cestith for those of you on Twitter), mr_mischief (obviously), mrmischief (not everyone allows underscores), Mr. Mischief (some places allow freeform usernames), mischief (but not the same mischief as here -- that's someone else), Pyro X (an old MUD and BBS nick), Lord Pyro (briefly, before I convinced the chivalry and heraldry-themed computer club they were going over the top), datawerx, groundhog (born on 2 February after all and this was my CB radio handle when my dad was big into that scene), and my Steam/Origin gaming nick pyrogroundhog (which is simply an amalgamation of Pyro X and groundhog).
For most everything that uses a nickname it's been some form of Mr. Mischief since 1993 or so. It's rare to find me without my middle initial when I'm using my real name, but it could happen here or there.