Breakdown: Human-Machine Interfaces
The physical buttons are large enough to activate but small enough to stay unobtrusive. They take firm pressure to activate so you don't need to worry about accidental activation. They also provide satisfactory tactile feedback.
The multi-touch screen is the true evolution for the interface. It allows for context sensitive and intuitive controls. It also allows you to interact with the iPhone in a fulfilling and responsive way.
The speaker provides adequate sound for phone, music and video use. It's not the ideal way to listen to movies and videos, but it works if you are without headphones. The only drawback is the volume: You do find yourself straining to hear in a crowded environment, so a little more volume in the speaker phone would be welcomed.
The microphone picks up your voice well. It also picks up some of the ambient noise. Not enough to make you unintelligible on the phone, but enough so the other party knows what you are doing.
The headphones are a great addition to the iPhone, especially right out of the box. They provide good sound and do a surprisingly good job at blocking out the ambient noise. They also have a button/microphone. Press the button once to pause music, twice to skip to the next track. You can also press the button to answer an incoming phone call. And since the button has a microphone in it, you can talk on the iPhone without removing your headphones.
Ergonomic Breakdown: Comfort Factors
Ergonomic Breakdown: Efficiency Factors
The multi-touch screen makes navigating and controlling the iPhone intuitive. When something is intuitive you're brain doesn't need to process that many things to operate it -- mental efficiency at its finest.
Controlling applications is efficient due to combination of universal and application-sensitive control schemes. That may sound confusing, but it works. A basic framework of controls, like flicking, pinching and tapping exist as well as standard placement for the navigation buttons (like back and edit). But only the necessary buttons appear in any given interface.
Furthermore, the button layouts are tweaked for some applications. Specifically with the keyboard. The keyboard for entering web addresses has a ".com" button instead of a space bar.
One of the coolest efficiency enhancements has to do with the text prediction of the keyboard. It has auto-correction and tries to predict the word you are trying to spell. It also adjusts the keyboard as you go. When you are typing and the iPhone thinks it knows what letter is coming next, it enlarges the contact area for the button and shrinks the area for the surrounding button so you are less likely to "press" the wrong letter.
Use, Misuse & Unknowns
The iPhone can take a pretty good beating as well. The screen fights off scratches and the machine can take some drops and keep on ticking. PC World has a great video on there iPhone stress test.
Long-term use is still unknown.