Using Photoshop for Good/Evil

Curbly guest Craig spied an old post of mine, Attention Woodworkers: Make this Pisa Bookshelf and got all evil genius about it. Craig made a schematic of workable plans for the bookshelf using Photoshop. Here's how he explains how he made the plans:
I take a photo of a shelf which is always at an angle, and use Photoshop to rotate it so it's straight, then make a new layer and trace it, then resize it to actual, and in PaintShop I can throw...