The Home Screen: This needs to be redone. I would much prefer to see a modular space like igoogle.com implementation. Each module is defined in usable areas and layout options can be selected for each applet. ie full module or collapsed Maybe even a tab structure that can be filled with application shortcuts or mini versions of the apps.
Screen Off Feature: There needs to be an easy way to turn the screen off and locking it but not turning off the device. I would follow the iPhone usability for this feature, where the power button turns the screen off and when you hold it down you turn the device off.
Finger Vs. Stylus: The finger usability should not compromise the stylus input. This can be address by using input size comparison. If you are using the stylus the input size and pressure is concentrated in a smaller area and if you are using a finger the input are is much larger and should enable a response system for finger use.