I can't speak for the grandparent poster here but for me, the killer difference between the N1 and the iPhone is that the browser is far, far faster in the N1.
The rendering speed of the N1 amazed me the first time I pulled up a page. It also has enough RAM to keep more than one page open at a time without having to re-load as you switch windows (as I discovered with the iPhone). This may have been addressed somewhat in the 3GS but I only had a 3G model.
I also appreciate OTA syncing for contacts and calendars that doesn't cost me $100/year.
The integration with Google Voice is also a plus (having it auto-switch your voicemail over, and make all outgoing calls through your GV number).
The speed issue is mostly a shortcoming of the 3G. The 3G is so slow under iPhone OS 3.0, I'd have a hard time recommending it to anyone. The 3GS doesn't have the same problem, but as I don't have a N1 it's hard for me to compare them.
The rendering speed of the N1 amazed me the first time I pulled up a page. It also has enough RAM to keep more than one page open at a time without having to re-load as you switch windows (as I discovered with the iPhone). This may have been addressed somewhat in the 3GS but I only had a 3G model.
I also appreciate OTA syncing for contacts and calendars that doesn't cost me $100/year.
The integration with Google Voice is also a plus (having it auto-switch your voicemail over, and make all outgoing calls through your GV number).