Build quality is exceptional.
Touch interface is remarkable.
Touch keyboard employs some interesting technologies to improve accuracy.
In ultra-mobility mode, it is faster to get online and get email and surf the web on the iPhone than the OQO.
The iPhone seamlessly finds and connects to any open wifi hotspot. Failing that, it uses AT&T's Edge network. This means you're always connected. There is no sense of being online or offline.
Google Map is actually useful on the iPhone. It is easy to get to. Integrates well with touch (pinching in and out to zoom in and out works well). And displays live traffic info all the time thanks to the iPhone's always-connected ability.
Outlook integration is done very well. I was hesitant to purchase mainly because I was skeptical about Outlook integration. However, calendar events, contacts and even your mailboxes are all synced quickly and efficiently using iTunes. The only thing that isn't synced are tasks.
Browsing on the iPhone's 3.5 inch screen is remarkably usable thanks to Apple's ingenious intuitive touch interface. The phone intelligently interprets single and double taps to automatically scale up or down a web page to exactly fill the screen, leaving no wasted space around the borders.
I'm very interested in the touch UI on the iPhone. Microsoft and UMPC manufacturers in general can learn from what Apple has accomplished. It is obvious that Apple designed the iPhone from the ground up with touch as its primary interface mechanism. Unlike other touch devices, the iPhone has solved many UI problems associated with touch and it is clear that touch on the iPhone was not a bolted-on afterthought.