Please feel free to make as many comparisons between the 3GS and N1 as you like. I'm very interested in the pros and cons. Don't be shy.

Thanks!
Sure!
First off, the screen, there is no contest. The iphone looks horrible after using the N1. The phone is crazy fast with the snapdragon chip. It feels great in the hand (not that the iphone didn't).
I've owned the first iphone, a 3g, and a 3gs. So i have had a lot of time to develop iphone using habits. Some things are hard to change over. The keyboard layout is a little different, no big deal. There is no hardware silence switch. The trackball button doesn't wake the phone up (only the top switch does unless you're rooted).
Lets see...
A removable battery is very nice! Having removable storage is great too. The google integration is incredibly nice.
The nexus one live wallpapers are very cool as well!
Battery life seems just fine so far (I haven't had it a full day yet but i've been playing with it non-stop for hours with little drain).
The phone's build quality seems spectacular so far.
My impressions of android are great so far. I cannot believe how terrible apples notification system still is. Seriously, after 3 years we still have obtrusive pop up windows, it's inexcusable to me. I had lockinfo + GRiP on my iphone just to tolerate using it. The girlfriend had a pre and seeing those notifications versus apples made me angry! So far androids notification shade is fabulous.
The nexus multitasks seamlessly. It really is pleasing.
The browser is better in my opinion partly due to the larger screen and faster processor.
So far I can't see any reason why I would return the nexus or go back to the 3gs.
I will say the iPod application is better and i'm having some difficulty deciding what to do about mobileme, but for now, it's an easy decision for me.