The answer is Newton! Yeah, it may seem like I'm biased looking at the avatar I'm using, but I speak from the perspective of having used almost every PDA and desktop environment of our days.
The thing is that Apple actually did what you wanted, they started from scratch with the pen interface in mind and poured lots of money into it.
It is not easy to explain the user experience you get when using a newton, take a few minutes to watch this video. It is the first newton model (launched at 1992!):
http://www.youtube.com/watch?v=64QuJdJmCbA...related&search= That's "whole-screen" handwriting recognition, printing to hundreds of printers out-of-the-box, application inter-operation, etc. Look at the way you select text!
These are the user interface guidelines published by apple, there's some philosopy in it!:
UserInterfaceGuidelinesOS2.0.pdf Read at least the first pages of chapter 1, and I'm sure that the next time you're developing a program you will remember it.
Screen resizing? no problem, this
picture is a screenshot of the newton emulator running at 1024x768, no modifications done to the OS ROM. Some more screenshots
here enough ranting :-)