Dan Staffer, in his book Designing for Interaction has a great bit where he talks about Mihaly Csikszentmihaly’s philosophy of Flow and how it relates to adaptive devices and applications:
Flow, and ideally, adaptation, involve finding the correct balance between the challenge of the task and the skills of the user. Too much challenge produces anxiety; too little produces boredom. Adaptive devices and applications, if well designed, help users achieve this balance, this flow.
I think this is a great way to look at design in general and the balance of form and function. For more on Flow (which is a great concept and too much to cover here) check out the wikipedia entry on it.
