I have an order for a dark chocolate cake iced in ganache. I would love to pipe verticle ruffles on the cake. I have never piped more than a border with ganache before, so I am wondering a) will the ganache hold its shape to do a ruffle cake and b) if so, what would you suggest for the ratios of chocolate and cream?? THANKS!

I would think it would hold its shape. You can throw it in the fridge and let it harden back up if you want to ensure it. The ratio for dark chocolate is 2:1, just like milk chocolate.