Right after installing VS 2012 RTM I tried my luck with a new WinRT app, but the XAML designer kept crashing on me. Given the fact, that it was not the most robust feature during the CTPs I was not really surprised, but this time it was simply unusable.
Looking around I got a working solution from the blendinsider blog.
Works quite well now!
Thanks to Unni Ravindranathan for finding out!