A common problem in iOS development is the keyboard sliding up in front of a text view, blocking it from the user's view. There are a number of third-party libraries that handle this problem, but the core concept is to move the view up when keyboard appears, and slide it back down when the user is done.
Most non-game iOS applications will have a table view somewhere. Many of these table views are simple enough that the cells are identical (except, of course, for their contents).
There are many circumstances where you want to present modal views in an iOS app. The one that confronted me was a Login form the first time a user opened the application (and technically, any time thereafter if she never successfully logged in).