I built a similar (albeit not drag and drop) designer for an intranet seat-planner application eight years ago. Really like what Eventbrite are doing though. They're killing the ticketing space.
AMA: I worked on the frontend for eventbrite's seat designer tool.
Another really good raphael use-case.
Related to this is Social Tables (https://www.socialtables.com/), a DC-based startup making some really cool event-planning software.