I just heard about this.

PixelOz has written a an E-book on making paper models:

This is a free e-book that I just finished writing about how to design paper models (card models). It is based mainly on the freely available open source program Blender 3D and an illustration program of your choice but it teaches a lot of the most important fundamentals of 3D paper model design that have the tendency to give a wee bit of trouble to new designers. It is 227 pages long and has hundreds of full color illustrations to help you understand the concepts of the e-book better.

Seems to cover a different style of papercraft than is usually found on NPT, but looks like it might still be useful regardless of your preferred aesthetics.