When I first started registering at various internet places, I was around 15 or 16, and I really wanted to use the same "name" everywhere. Just wanted to create some sort of a fantasy name for myself. I came up with Mora (a shortened version of an even earlier, "Elvish" nickname); and I wanted to use a fantasy "surname" too, and I went with Winterheart. But then I thought "oh, crap, everyone will think I got it because I'm a Sonata fan" (Sonata Arctica has an album called Winterheart's Guild), and I switched "heart" with "soul".
It's childish, cheesy and a little silly so therefore, it fits me well after all these years
I use it on my last.fm, my tumblr, and some other places too I think. There's one forum I post on under my real name and that took me a lot of courage because I thought people would bug me on my Facebook. And then I thought "hey, but I like having various forum people on my Facebook, and I can ignore the ones I don't like".