Ok. Now that I've had 12 hours with the phone (though to be fair, for most of that time I was asleep), and am on a real keyboard (the built-in keyboard is very smart, but I'm much faster with a full sized one where I can use all 10 fingers), I can make a full report.
You cannot (yet) assign an iTunes song as a ring-tone. That's kind of a bummer, but it's so obvious that I do expect them to fill that gap with a software update later.
Turning the phone sideways for landscape mode is very cool, but it only works in selected apps. It works in the browser and in iPod (though videos always play landscape). Where it does work you can flip it left or right (that is, with the home button on the right or left side of the screen) and it works. You cannot flip the to upside-down portrait mode (it stays upside-down).
I've browsed a number of websites and, for the most part, they all worked just as well as they did on my desktop machine unless they required flash or java. I'm unconvinced that Apple is going to completely have its way about a plugin-less web. I think they're going to have to buckle under and support one of the two (and I'm pretty sure the obvious choice would be flash).
The phone functionality is very nice, and visual voicemail is the topper. My only complaint is that the speakerphone is very, very weak and there is no voice dialing capability.
Voice dialing is sort of a double-edged sword. It was never very reliable for me on my RAZR, but it was much safer for driving. The iPhone is going to be a lot more trouble for drivers not only because of the lack of voice dialing, but because the touch surface is, obviously, completely lacking in tactile feedback (that is, you have no choice but to look at the screen to know where to touch). Fortunately, I have a GPS with a built-in speakerphone, and thus I can at least interact with a touch screen that will be positioned near the windshield.
Since I have a GPS in the car, I'm not sure I'll have too much use for Google Maps. But the one improvement is that it can display real-time traffic information. Adding that to my GPS would cost me about $10/mo, plus buying a traffic dongle.
Typing complex passwords in with the keyboard can be amusing.
I guess having youtube built-in sort of makes up for the lack of games (at the moment). Unfortunately, most of the web based games I play with require flash. The big thing I occasionally count on from my phone is entertainment when I have to wait for something. While I was in line for the iPhone, I played Tetris and Bejeweled. Now, if I have to wait in line for something, I can surf the web.
One big blow is that I have not yet found a way to turn on the ability to use the phone as a hard disk. This used to be the big reason I had an iPod - I could always plug it into a machine and use it to sneaker-net files around. So far as I can tell, that ability is absent on iPhone.
Another was that the iPhone will not act as a dialup modem for a laptop. In fact, though you can discover the iPhone via bluetooth, there's nothing at all you can do with it. It appears only to be able to use bluetooth to set up a handsfree connection, at least right now. Given that you can, theoretically, move up to 7 GB of data across to the phone, syncing over bluetooth would probably be too much to ask. And since it is so Internet connected, you can, for example, use e-mail to move pictures out of the camera.
Another missing point is that the WiFi capability is limited to accessing the Internet. You can't use it to print or browse local shares for files or anything of the sort. Of course, if you have web sites on your intranet, they are accessible.
The biggest difference of all, though, is that this phone is very likely to receive software updates as we go along. No other phone I've ever owned got a software update ever, even if the same model often got updated firmware in the retail channel. So maybe some of these deficiencies will be addressed later on.