Chapter 3 of the book Design Interactions was called "The Zen of Palm".  On page 216 is an excerpt of what I found to be simple yet profound:

Rob articulates his design approach as a philosophy, but he also supports his philosophy with a very pragmatic design process: first understand the customer, then prioritizes ruthlessly:
One bit of advice that I gave to people designing the Palm OS was, "If you can really understand the one thing your customer wants to do most frequently, and make that a one-step process, then I guarantee people will like the product."
     Just say, "What is the one thing you want to do?" and even if you have to throw out conventions of logic, architecture, and hierarchy, you should make that one step.  The more "illogical" your approach is, the less likely it is that it will blindly follow the conventional wisdom, and hence the more likely it becomes that you will be able to differentiate and create a successful product relative to your competition.  If you take the conventional approach, by definition you're not innovating.  If you just say, "Here are all the features," and you lay them out in a logical pattern, then that's not going to be a successful product.

Before the iPhone, my mobile device of choice was the Palm Treo 650.  I used to love the Notes app and the To Do list app.  And to this very day with something so simple as a to do list app or a notes app, I haven't been able to find a third party solution where I was satisfied as much as the Treo.  I am convinced that it is because I experienced the ingenuity of the applications that Rob has designed in the palm with his philosophy of: "really understanding the one thing your customer wants to do most frequently and make that a one-step process".  I find it very interesting that similar applications have come out years after the palm but it does not meet the quality of design that palm had in its software.  And he hits it right on the nail.  Some of the most frequent things you want to do with software take several steps to complete.  And today I still wish I had those applications on the Treo that the iPhone doesn't have. 

Rob Haitani, you are a hero of user interface design in my book.