I think I understand why Apple choose to go with the single home button for iOS devices. I think the argument for it is much stronger than the single button mouse. The problem is that they once again didn't live with the limitation they set for themselves. They added double-clicks.
Double-click are much worse than a second button. We’ve known this for years. A number of users have trouble executing double-clicks, so it should only be used as a short-cut. Many other users have trouble understanding the difference between single-clicks and double-clicks. So many users have been mistakenly trained to always double-click. So, we have to program defensively to recognize and ignore double-clicks even when they don’t do anything. Not to mention that some developers fail to understand how to properly use double-clicks, which just leads to more confusion among users.
I like the “recent apps” UI in iOS 4, along with its audio and other controls. What I don’t like is having to double-click to get to it. Worse, double-clicking is the only way to get to it. Though I suppose you could argue there is (almost) nothing the user could do through it they couldn’t do another way.
I think what I’d really like would be three buttons: Home, Spotlight (search), and Recent Apps. Without two more buttons, though, perhaps there’s another way to make it work better.
Consider this: When you are in an app, pressing the home button takes you to the last home screen you were on. Pressing the home button again takes you to the first home screen. Pressing home again takes you to Spotlight. These are not time-based double- or triple-clicks. These are just sequential uses of the home button in different contexts. Given a single button, I think I’d like my first press of it to take me to the recent apps. Pressing the home button again would then take me to Spotlight. A third press would take me to the home screen.
Although, I’m not entirely sure about the order of the last two. Since the recent apps only takes up a strip at the bottom of the screen, perhaps an on-screen Spotlight and Home buttons could be added to allow the user quick access to both. Then the home button becomes simply a “recent apps” button.