You might not find that particularly interesting, but we found one aspect quite intriguing. It was the method of design. While one might simply obtain the dimensions of an iPhone and then design around that, the Intstructable did something a little different.
A library search revealed a complete, accurate 3D model of an iPhone (at GrabCAD). This model was imported and then the case was modeled directly around the 3D iPhone model. No measurements, just use the "actual" item.
We think this technique could prove quite useful for a number of other 3D modeling challenges.