This is the stuff that matters to me. 

Keyboard:

I happen to like the iPhone keyboard much more even after typing a lot of hours on the android/nexus one.  The buttons still press where I don't want, and doesn't recover from typo's quite as well.  Although, a huge factor that can help counter the bad keyboard, is the fact that there is a microphone built into the keyboard app so you can do voice to text on any text field anywhere in the phone.  I use this every day and it works well!

OS Differences:

Android has as many pro's as con's - it's a close fight.  iPhone seems to be snappier, more responsive, and more likely to do exactly what you want when you want.  Android has more power, can do more things like built in tethering, HDMI support, many simultaneous background services, and a much more plugin ready framework.  I can install 10 communication programs that can all do email, and when I go to write an email it will ask which app I want to use, you can also set a default.  This is much more the way a desktop computer works compared to iPhone - not allowing another mail program.

If you are a 'standard' user you probably won't know what to do with these features - and probably enjoy iPhone a little more if you tried them both.

Apps:

The app market place that google is supporting for android is really well done, easy to use, and has a ton of apps.  Pretty much anything you could find in the iTunes app store, you can find for android.  There are tons of apps for android that you cannot get for iPhone.  I have some apps installed that do some cool things:

• Backups - every night it packages up the user data/apps on the phone and ftp's it to my server for backup.  It can easily restore from this too! (no more itunes)
• Auto-Contact - When I end a call with a new number it offers to make a contact with a background service that is running.
• Auto-Responder - I turn this on when I'm busy and the phone will txt people back when I miss a call and send a pre-configured message.
• Pandora - runs in the back ground, has a desktop widget too - works well.

I have to point out at this point a huge con for android.  Due to the quality control at apple, and the iPhone NOT allowing background processes, the iPhone was much more stable.  I have bugs in my nexus one from time to time - I know it's due to the 3rd party apps, but I will have to spend a lot of time removing apps and testing to get this phone as stable as my iPhone was.  More open platform also means there are some buggy apps in the market place.

App quality:

I can say the facebook app on android is not half as good as the one on iPhone.  Also, the remote desktop app I used on iPhone was a much better product than I could find for the android.  That said, there are a lot of apps I'm using that work perfectly well, and don't exist on iPhone.

Communication Issues:

This is probably not an android issue but this phone gets slightly less reception than my iPhone did most of the time.  I easily drop more calls now.  I have the AT&T version of the N1.