I got my iPhone in the mail after 10 days, beating the 2-4 weeks delivery estimate. I've used it for a week and have some opinions I'd like to share.
The biggest suprise is just how good video looks. Everyone I show it to goes "wow". This is something you have to see in person. The video quality for "video iPod" mode and for "WiFi YouTube" mode is basically perfect. When running on EDGE, YouTube downloads a lower quality version of the video that has visible artifacts, and looks more like typical video on a PC quality (e.g. similar to my Slingbox). In any case this is a seriously good video player, and I happily watched several complete TV shows on it.
The built-in speaker is also surprisingly good, considering the limitations of a mobile device. I left the iPhone lying on the table and used it as background music.
The user interface is easy, no-one has any problem using it immediately, and typing on the keyboard is much easier and more accurate than I expected.
My main disappointment is with Email. It works, but I've got used to the Gmail client application on the Treo and Blackberry. The generic pop client just doesn't work well enough since it doesn't understand archiving and threading, and the safari browser version is inconvenient and slow when using EDGE. I really hope that the Gmail application is in the works for a future update, it seems likely, given the relationship between Google and Apple, and the Google Maps application that is already included.
For use at work, it can't yet replace my Blackberry. The iPhone VPN doesn't work with the VPN where I work. The LEAP security mode we use for wireless is also unsupported, although it works fine on my MacOS laptop. Using a simpler guest wireless setup I did see over 3Mbits/s in a speed test which is very impressive for a mobile device.
I can use Safari to get at Outlook Web Access, and http redirect based secure access to internal web pages worked fine. I have had no crashes or problems with Safari, trying it out on several sites.
For detailed insight into the iPhone, go read RoughlyDrafted, its by far the most thoughtful and interesting blog on the subject.