Might get one at some point as I want to get play with some android openess goodness but android seems slightly fixed - no firmware updates, the android gets new versions but their not passed along on to the handsets unlike the iPhone where the firmware upgrade is available for all handsets as soon as a new version of the OS is released. Also quite a few bugs with the nexus I've heard.
I think jermin is right it needs to be compared to the iPhone V4 (not 4G- I doubt it'll be LTE or wimax capable - it'll be EVDO capable so it can go on the verizon network in the US)
However if giffgaff rewards can be in google money then I'll get one
Thanks jermin and bigfatbball2 for the comments. I'm not sure if the Nexus One (sounds like a spaceship?) is an iPhone-killer. I think you're both right, the next iPhone (expected this summer) is expected to up-the-stakes yet again in terms of handsets. Let's wait and see!
I think if your life is wedded into Gmail, Calendar, Maps and Contacts then the Nexus One does a top-job at integrating all of these together in one convenient place. Google Voice also works (mostly) quite well on the Nexus One, although at the time of writing, this has now been released on the iPhone too.
Technical aspects aside, at the end of the day people will prefer one or the other's styling and navigation - it all comes down to personal preference.