Someone clever once said that modern analytical philosophers would wear lab coats to work if they thought they could get away with it. I think something similar could be said about software engineers.
How do you implement a custom UIView class that needs to draw over its contents? A quick tutorial that uses custom CoreGraphics, a customizable content view, and a neat trick to preserve the drawing hierarchy and your sanity.
Most developers think of Agile techniques, (namely development methods based on iterative and incremental development) as pertinent only to software engineering.
It would be interesting to examine the history of software engineering via solely the history of the process of layering build systems atop each other.
I probably reference this more than any single other Objective-C reference.