Photoshop CS5, several billion hours (More like 15-20, and most of those hours spent redoing things)
It's at a stage where I don't want to touch it anymore, aside from the last minute details that I'll tack on sometime in the next couple days. Thanks to all those who helped on making it as pro as it can be.
A note, for those still figuring out digital painting: Don't be afraid of shoving everything on one layer. I'll say this, that line up has 8 layers, the background, and those 7 characters. (Granted there's like 3 backup layers for every girl, but they're not comprised of several layers).