A-minus
To answer the question I hear most about it: yes, I love my iPhone. It is every bit the gee-whiz, fun-to-use, eye-candy-rich, conversation-starting geek toy I expected when I bought it. It does so many things so well and has fast become an indispensible tool. It also simplified my life: I have shed my pocket day planner, streamlined my contacts list, and I no longer lug my laptop away from my desk, since I can just whip out the iPhone for the majority of what I want to do online.
What's great about it is that so many of the "wow" features in the iPhone are actually practical. Pinching and spreading to zoom in and out: wonderful. Scrolling around a screen by dragging displays with one finger: so great I keep wishing my computer supported the same function. The touch screen is an easy, intuitive way to do, well, everything, and the relatively transparent access to the Internet (even on AT&T's network) turns the iPhone into an iAnything. Web browsing is great. The iPod is great. Google Maps is phenomenal. The weather pane seemed like a throw-in when I got the phone, until I found myself checking it a few times a day, and now I can't live without it.
That pretty much sums up the whole user experience: once you have an iPhone, you immediately find it useful and pleasant, and everything else pales in comparison. In a word, terrific.
Alongside my praise, I am not afraid to admit it's not a "perfect" device, in the sense that all of its capabilities are not pinnacles of joy and ease-of-use. I will defer to the many, many reviews of the iPhone elsewhere online for a reasoned critique, but here's what I personally am crinkling my nose at:
~ The vertical keyboard layout is mediocre. I might enjoy it more in horizontal web layout, but since it's not available anywhere else, I just do all my typing upright, and three weeks in, I'm still tapping words with my index finger. Yeah, it works, but BlackBerry and Treo users (including myself) will feel slowed down by its interface. It does trump T9 on a phone, but that's not enough.
~ Neat, look at the wheelie calendar scheduling interface! I use this all the time to show off how nifty the iPhone is. But as an actual scheduler, it's pretty damn annoying. If I used my Mac to book appointments I'd be in good shape, but I generally plug them straight into my iPhone, and man, wouldn't it be nice to have a 10-key number pad for dates and times.
~ Holding the device steady enough to tap the touch-screen camera shutter is a challenge. I could probably learn to juggle on a unicycle in the time it will take me to learn how to never blur my photos.
~ I worry endlessly that the spam-filter-less mail function and the fun but error-prone slide-to-delete finger stroke in it are exposing my email address to happy spammers around the world.
~ I've noticed that the side of my thumb is not a sufficient surface for the screen to pick up on tapping. This might just be my freak thumbs, but whatever the reason, it's annoying.
So, no, it's not perfect. I'm looking forward to firmware updates that continue to improve the UI, although I'm expecting them not to address all my concerns. The iPhone simultaneously reminds me of why I continually buy Apple products... and why I don't use the applications in OS X outside of iLife.
All this said, the iPhone is still a fascinating device and a complete game-changer in the world of consumer electronics. I am gleefully obsessed with it and proud to own it.