Programmers learn in different ways. Some need to read a step-by-step "how to" guide, others get by fine just using the official documentation and header files. Some are more comfortable attending a workshop or watching a video, others prefer to just dive in and write code.
Reading other programmers' code is another great way to learn about developing in a particular language or framework. A lot of programmers find reading strange code to be difficult, but it's a skill that I think is really important and I encourage every programmer to become comfortable with.
The folks at Web Resources Depot recently published 20+ Open Source iPhone Applications To Learn From which links to a bunch of open source iPhone apps that run the gamut from the official WordPress app to small utilities and games. If you learn best by reading code, or you want to improve your code reading skills, check it out!