I find the Nokia 2160e user interface intuitive. Ease of use does not matter that much, anyway. Rather, many people I know, myself included, have exhausted their willingness to learn yet another gadget user interface. This is the same mentality that millions of VCR users have. They refuse to set the clock on their VCRs, much less explore the advanced features.
Synchronization is critical.
Technology has a marvelous knack for forcing great ideas to get better before they are widely applied. It's still a pull world. We proactively get what we want rather than passively wait for someone to dump it on us. Maybe I have it backward. PDAs should become phones.