Apple touts their new iPod Shuffle as the ultimate in simplicity, as it has no buttons. However, having too few buttons doesn’t make it simpler, when each button has multiple functions and Apple needs to post a knowledge base article telling how to use all of the functions.
The new iPod Shuffle uses a controller built into the earphones to access all of its features. The controller only has 3 buttons, but the Shuffle has a lot more than 3 functions, so each button has to serve multiple purposes using various combinations of clicking, double-clicking, triple-clicking, and holding. Most people will need to carry around a reference card to remember some of the more obscure features.
The iPhone uses a single button on the earphones which serves to pause, resume with a single click, and skip with a double-click, with the volume control on the iPhone itself. That set of features was still manageable, but when a later software update added triple-click, it started the trend to unnecessary complexity.
Ideally, it shouldn’t be necessary to use any more than a double-click. Adding dedicated fast-forward & rewind buttons would make it much more usable.
For another opinion on the buttons, see Jordan Satok‘s post.