I was scrolling through these comments and noticed your question hasn't been answered...not really my place but since this piece was done for me I guess I can answer? In case you were still curious, it was done in Photoshop CS6.
As I said via email, I don't think I can adequately express my adoration for this piece. When I first saw it I just sort of stared blankly and then did a weird sort of flail-dance at my desk with a giant grin on my face that startled my roommate quite a bit. (That sounds so dull, I know, but people who know me irl could tell you that means I'm Very Happy.)
Thank you, thank you, thank you! I love it to bits and pieces. I will print off a nice shiny big version and hang it on my wall and cherish it forever. It's also my current desktop background, and I imagine it will be for quite some time!