Printrbot Printrbelt is making some nice progress. It is a continuous conveyer belt 3d printer that can print some long objects. New videos and features are released and here is a short overview.
Here is a 6 foot long sword:
Here is Wiliam Steele from Polar3D showing how the software control is implemented on Printrbelt:
Printrbelt producing many smaller objects (gliders) in a series: