The following sites gave me errors with my username, and if I changed the username to something unlikely I got the same error. I take this to mean that there's no evidence that username exists on that system. (And, I'm dubious that I'd have signed up at these sites.) * quizlet.com * www.enjin.com * apps.runescape.com * smule.com * livelib.ru
And, fiverr.com's URL for my username just bounces to the homepage, as did any username. (Again, I wouldn't have signed up there.)
Other than that, very cool.