I've used Palms, a PocketPC (for a short while) and recently a phone with touch screen, and frankly, I sorely miss the qwerty kb on the C1000.
I've heard of how the kb made the major diff, but never really knew it was that great.
For me, onscreen keyboards are just not good enuff compared to qwerty buttons. Of late, I've not been using my Z, but only because of a change in my daily regime. Also, I'm trying out the (not so) latest UMPCs and figuring out how it can fit into my regime.
So, chances are the iPhone 3G will not be my next zaurus.