Everything you know about design is wrong...
...when running your app on a small, high screen-density device.
As you may know, we are developing a GTD application that runs on the Blackberry Playbook and Android tablets (others to come) called Conqu. When we started, back in November, we were making designs as normal with Photoshop at the right size, and what we liked the most when looking at the designs (even when made small to fit the size of the device) were usually not all that good on the device. Since we hadn't developed the app yet, we only had mockup images to see. So what we did was browse those images to see how the actual app would look like.
This is what we learned.