I have not achieved a state of mental flow in over a year. If a place I'm
  interviewing at has adopted the open floor plan, it's a deal breaker.

I hear you. As an aside, does anyone know of any dev shops in Sydney (Australia) that don't use open-plan setups? I've been going for nine years, and I've only ever seen one (Campaign Monitor); the rest have been benches, or benches separated by low walls.