I'm in the UK so I definitely fit into the 'I don't have one category' and will probably never use the rev 0 software. While there are certainly some things I'd like to see change (mostly additions, some of which I'm pretty sure will be added) it seems to me Apple got a lot of the fundamentals right. With an eye firmly on that, here's my list of 10(ish):
1. Simplicity of UI - app launch and task switching - always two buttons.
2. Simplicity of UI - access to most stuff (especially frequently used functions) isn't buried in menus, the contents of which are invisible until the menu is opened - most actions involve tapping a clearly visible on-screen button. There are exceptions where appropriate of course (video is obviously much better full-screen).
3. Speed of the UI - transitions, app launch and using apps - all seem pretty snappy.
4. UI is gorgeous. Launcher and every app look classy. Love all those
transitions and screen effects.
5. UI is flexible. Where other devices have physical buttons (including numeric or QWERTY keyboards), the iphone has on-screen buttons. The buttons you need, when you need them.
6. Input - innovative multi-touch, finger-based input. Completely stylus free.
7. UI designed for capacitive touchscreens. Capacitve screens are great (high durability and clarity) but you can't, as I understand it, just throw one onto, say, a Palm OS or WM device. They need to be touched with a conductive object with a reasonably large surface area, like a finger. A stylus won't work. The whole UI has to be designed around finger-based input.
8. Battery life/power management - excellent esp. for audio and video.
Engadget got 9 hours video and 29.5 hours music playback. Crucial in a phone that these don't deplete the battery too much.
9. Settings - all gathered together in one place, as they should be (a lesson Nokia definitely needs to learn).
10. iTunes integration. IMO, iTunes does a great job of collecting together multimedia functions (ripping CDs, buying music (and video), downloading podcasts, managing (and playing) your music and video content, transferring and managing iPod/iPhone content etc). Without this integration I need an iPod as well as a phone.
11. Out-of-the-box Mac support.
Like I say, there are certainly things I'd like to see added (3G radio, exposed file system and much improved file handling, more BT profiles (including sync - at least for PIM data), to-dos, better alarm configuration in Calendar, cut and paste, multiple selection of emails for deletion etc, etc) but as a platform, especially for the first generation, it's looking extraordinarily good - IMO