I had a Nexus one also. I purchased it on the advice of a friend who, was a long-time Iphone user (
personally I think he wanted to just check the phone out himself without having to commit to buying it).
It was the first phone I had ever had of this type. A lot of people on the Nexus one and Android forums don't like Apple and think everything is too closed with them. I never got into the Apple vs. Android thing, I just wanted a phone to do what I needed for my business. The N1 did everything I needed and then some. T-mobile's packages were very affordable and, cheaper than what I had at Verizon. It had it's glitches but, was really awesome after upgrading to Froyo 2.2.
The customization on Andriod was pretty cool and I liked how you could view the weather on the notification bar at the top. Google voice is pretty cool too and integrated into the phone. The voice recognition is awesome also, you could speak navigation directions or texts msgs. The free GPS with Google maps was nice also and, the car dock for the Nexus one, along with the car home app blows away anything made for the Iphone, it's not even close IMO.
The Iphone 4 is much smoother in operation. It never locks up no matter how much I play with it. The battery life is outstanding. I actually love the Itunes integration very much. I used double-twist on the N1 but it's just not the same and, you can't get all the songs from the Itunes library. The app store is what the real big advantage Iphone/Apple has for me. I never understood until I started using it. I'm a onsite network and computer consultant on the side and, the Time-master App is awesome. It's just what I've been looking for and, without getting into details, I'll just say it's great for my business.
All in all, I've always wanted a Iphone. I wanted one since it came out but didn't want to switch to At&t. I found out that I could cut down on my data plans - which I didn't need as much as I had - and save. I also get a discount from At&t because I work for a specific company so, my bill is even less than what I was paying at T-mobile. Two years from now, when my contract is up; I can't say I wouldn't switch back to Android. It just depends on what is out by then, I'm sure a new Iphone will be available also. Right now I'm happy with the Iphone 4.