displays – Are there guidelines or best practices for designing multi-monitor systems?

By multi-monitor, I mean systems that arrive with multiple physical monitors, each with a predefined feature. These are usually industrial systems using their own software.

This type of system raises interesting questions, such as: Do we duplicate important elements on all screens? Are all screens dimmed to display a modal dialog on any of them? Do we create an "importance" screen hierarchy or are they equal? Etc.

Research has been done on this from the point of view of ergonomics, but I am looking for a more work focused on the user experience.