Using Joe Hewitt's excellent iUI package, yesterday I built an iPhone-friendly interface for TeamMarks, an application I'm almost but not quite ready to launch. (It needs a permissioning system first.) For now, just think of it as del.icio.us for Google Apps but with folders. And permissions. :-)
Developing for iPhone feels a lot like writing Newton applications. You don't get to use the same development environment as the Apple engineers (then it was NewtonScript vs C++, now it's AJAX vs Cocoa), there's no emulator so you're stuck testing on an actual device, and there's no good way to take a screenshot.
I sincerely hope that by the time of the Office 2.0 Conference, Apple will have released the tool that Steve Jobs used during the iPhone debut keynote to mirror the iPhone's display on an external monitor/projector. Otherwise there are going to be some really clunky presentations, mine included.
Update: iPhoney isn't perfect but goes a long way toward addressing the screenshot problem. Cool!