Smashing Magazine posts a great article on some principles for including animation in mobile UIs. I think the use of animation is under-estimated by some HF people because it’s hard to quanitfy the “performance benefit” (e.g., they may not increase the speed at which a user completes a task).
Some notable examples of animation are the infamous Apple’s page bounce-back, the page-curl in e-book apps or the bouncing icons on a Mac (or expanding/minimizing windows on Mac/PC). Difficulty in quantifying objective benefits may lead some to dismiss animations as superfluous and unneccessarily ornate. I wholeheartedly disagree. Animations provide a fluidity that makes interfaces feel responsive even delightful.
The article provides a lot of reasons for the benefits and most appropriate use of animation. It’s typical Smashing Magazine (i.e., LOOONG) so save it to read later!
(post image from the article)