That's an interesting question. I'm a member of 2 or 3 other forums where I use a different name. I don't really know why I've done this, but on these other forums I've used a contraction of my real name. It's only here that I call myself Woody. Btw I know nobody is interested but I use the tag Woody because I'm a great fan of the novelist / humorist P.G. Wodehouse.
Incidentally I lurk over at Wilders, So I can easily recognize Humpty and Hazel under different names.