I picked openheart because I needed something that was gender neutral.
At the time I joined a few months ago, I wasn't ready to commit to anything, and I was trying to be careful not to present myself as something I'm not while I figured out who I was. (The main question: Am I a woman or do I just want to be one?)
I also don't want a name that would connect people to my legal (and still-closeted) name and I hadn't yet picked a name I was sure I'd be happy with (though as time's gone by, I seem to be stuck with Kristin...was the first one I told my wife about and though I might choose differently were I to try again, it's a name I like and it has the benefit of having not having strong associations from my past. I knew of a couple of Kristins/Kristys in school but none were in my grade, etc.)
Um, so back to my username...I wanted something kind of feminine but not gendered. And I wanted something I could use for a new Gmail account (though I had to add numbers to it there), because I didn't want to risk using my main e-mail account and be to too easily identified by my legal/everyday name. Damn closet!