The design is almost completely a ground-up build from scratch, tons of responsive tweaks and optimisations for retina support. I'm a Frontend Developer by trade which has helped, the only thing that I'm currently not happy with is the amount of "over-rides" I've been slinging in as I build, at somepoint the template will be rewritten again for sake of pedantism and optimisation more than anything else.
Give us your verdict.
I'm currently in the process of finishing up a completely "integrated" Magento installation which is still physically separated (databases aren't shared). Effectively, the Magento installation looks so close that to users it will be seamless, by the end anyway. Though this is still heavily in development, I know you guys will want to see something of it.
Any points of improvement welcomed, it's all about growing.