I've used the name Half-Full (as in "the glass is half full") for about 7 years, but first used it in a chat room I still attend. It's for people dealing with autism (my son has autism spectrum disorder), and I started going to it the day after my son was diagnosed. The day of his diagnosis, I was overcome with, surprisingly, feelings of optimism, instead of the fear I would have expected to feel, so I chose a name that reflected my positive outlook on my son's future.
I find that, in general, it becomes harder with age (and the onset of cynicism) to stay true to my optimistic nature, so I've retained the name, and used it other places, such as here, to sort of remind me to think positive, even when it's not an easy thing to do. It's to remind me that all the times I've been most successful, productive and happy in my life, were the times when I was my true, optimistic self.
Anyway, that's enough hot air about me