With a few days away from the official launch, it's interesting to see how iPhone will fare in the marketplace. I'm expecting to see a well-thought usable UI and seamless integration with other applications like iTunes. Following the good tradition of Apple, everything is just going to work, right off the box.
One thing I'm not sure is the overall robustness of the operating system. Retrofitting OSs that were designed to run on a desktop for use in an embedded environment, with scarce resources, so far produced mediocre results. Contrast that with an OS like Symbian, built from ground-up with the ability to gracefully handle exceptions common in the embedded environments. One interesting metric to look for will be the average time between reboots.
Will the users care about reboots ? As the line between the phone (thus far perceived as a robust device) and the computer blurs, it remains to be seen.