Well, I have to say that I am happy to be back to my 3GS after spending 5 days with the Nexus One... It just didn't work out between us. Here is why:
Contacts
I like my contacts to be in groups. On the iPhone, it is very simple to switch between these groups. On the N1, it takes multiple steps and it gets to the point where I get irritated just going through my contact list.
Screen
The screen just does not have the same precision as the iPhone. For example, when I receive a new text message and press the Type to Compose box, I have to press that box multiple times to get the keyboard to pop up. Very annoying. Also, the bottom row of the keyboard is very inaccurate. Many people have already mentioned the issues with the soft touch keys, so I won't talk about it here.
Miscellaneous
I first thought that The General was ridiculous for mentioning the lack of the "rubber- banding" effect when scrolling lists, but I have come to realize that I actually love this feature. Not a deal breaker, by any means, but it is a useful feature that lets you know you are at the end of a list (no, I don't like to look at the scroll bars).
Lack of iTunes support is something I really miss. A lot of people do not like iTunes for some odd reason, but I have to say that when I was using the N1, I missed just being able to plug my iPhone in and let iTunes do its thing. None of this mounting USBs and drag and drop files onto an SD card crap. Call me lazy, but you cant argue how easy iTunes makes your life.
My car also has iPod/iPhone integration. Obviously, the N1 will not work and I would be forced to carry two devices instead of one.
Conclusion
Although, I enjoyed the excellent resolution of the screen along with the great notification system, they just weren't enough to win me over.