Ah, of course. I caved in. Since Friday evening I've been iPhoneified.
It took a bit of hassle with AT&T to get our account changed to a FamilyTalk plan (iTunes said we needed to do it first, AT&T said sign up separately first). Apparently the confusion came from the iPhone Activation Support department being closed. Or something like that. They were all perfectly polite and trying to help though (and eventually did).
The really brief review is: UI rocks. Software is a bit of "work in progress". Typical examples: MobileMail can read Word Docs, but not mails forwarded as an attachment or vCard files. The Contact manager is all spiffy with maps integration, but there's no way to send a vCard. No "highlight to quote" feature in the mail application.
If you've read anything about the iPhone you've heard about the lack of cut'n'paste, too. I imagine they didn't implement it because it's going to be hard to get right and slightly tricky to use almost no matter what they do. Better keep it simple for the initial reviews. My Treo 650 got a few software updates, but they "only" fixed some regular crashes - no significant feature improvements. I am confident that the iPhone software will get better fast.