To the OP:
I also made the jump to the Nexus One after owning an iPhone for about two years now. I had the 3G a week after launch day and the 3GS on launch day. I had them both jailbroken and unlocked. I would say that my knowledge and background on the iPhone's capabilities are above average.
With that said, you have to understand that the Nexus One is not a full multi touch phone. When you say you aren't able to tap an icon sometimes and have it respond, please make sure you don't have any part of your hand/fingers touching the screen else where. It is very sensitive to this. I noticed this about a day after I got the Nexus One. This is one reason why I love the iPhone, it is so much easier to use with one hand. If they enabled full multi touch across the entire OS, the Nexus One would be much easier to use with one hand, which I like to do.
The visual voice mail using google voice doesn't mean you have to change your number. What it basically does is direct your voice mail to your google voice account so that you can view the transcribed voice mail on your google voice app. You still get calls to the same number. Google voice is extremely well implemented with the Nexus One compared to what garbage they had on the iPhone. And that being a jailbroken app.
The typing/keyboard is a lot harder to use if you are used to typing like me. I use one hand usually to send a sms and the iPhone just blows the Nexus One away as far as recognizing what you are trying to type.
On the copy/paste feature, the Nexus One apparently isn't capable or perhaps the android OS isn't capable of copying texts from the browser like the iPhone does. This is something I definitely miss.
I also do miss the iPod on the iPhone but it is something I am willing to trade off for the functionality of the Nexus One.
Overall, the touch screen functionality on the iPhone beats any phone on the market at the moment. It is the smoothest most responsive. The lack of background processes on the iPhone is what made me decide to make the jump to the Nexus One. This could only be done via backgrounder on a jailbroken iPhone. I got sick and tired of having to update/jailbreak every time a new firmware came out.
If I had to pick what I miss the most or what I wish the Nexus One had, it would be the touch screen capabilities of the iPhone.
I guess I could throw in no volume rocker on headphones also =/