I decided to treat myself to a nexus one (unlocked, imported from the US, and on o2) a few months ago- upgrading from my outdated first generation iPhone.
While it's taken some getting used to, I have to say I've not stopped being impressed with this phone at every turn. The keyboard for typing is a lot worse than the iPhone, unfortunately, and from what I've seen it's like typing on a poorly designed blackbarry. However, the phone works great- the software is amazing, and the call quality is perfect. I've only had a maximum of say...3 minutes of 3G reception since I got it but I think this may just be bad luck (on 'edge' or '2G' it is impressively fast). The apps are excellent, and the customizable home screen went down a treat. I've not got much love for the often touted "live wallpapers", though.
Comfortable to hold, easy to work with a laptop (so much so that I accidental ran my laptop as a blue tooth head set)- but you might want to buy a bigger micro SD card!
Battery is average for a phone of this type. I've been running 'flash' on it for the last few hours, and over wi-fi it is crystal clear, responsive- but some things are not supported ("does not support this device" or, just crashing) but it is in beta, to be fair- and a lot of flash based applications could prove difficult to use as you can not right click, or use the keyboard.
The music player is good, facebook app is a little useless, but with lots of free apps you can't go wrong!
I'd recommend it to anyone.