Came from HTC Thunderbolt, which was said to have a notorious battery life.
Back in my first day of Thunderbolt (with early version of stock rom), I couldn't last a day work at my job with mild-moderate use of my phone. Then, it has been getting better and better as devs came with custom roms. By 12/14/2011, I have been sparing 30~40% of standard battery on my Tbolt when I was leaving my work.
GN seems in need of a little bit of tuning in terms of battery. My personal feeling on the first day? It feels just like the first day of my Tbolt. It barely last a day's work. Seems like it's dropping approximately 7% an hour with mild usage (I work in a REALLY WEAK signal area which consume more battery than usual). Moderate usage may cause 10~15% drop an hour. Even though my GN will last a day's work of mine at this moment, considering that it comes with 1800mAh battery, I expect a little better performance. I, however, believe this battery life will surely improve as the updates and custom roms come out.
For those who transitioned from D1, D2, DX, and other 3G phones, please be advised that this is 4G phone. You were driving a naturally aspirated engine vehicle before, and now you are onboard a turbocharged engine vehicle (with nitrous oxide?). This will give you a significant speed enhancement, at a cost of battery life. I also came from D1 and DX, before my Tbolt. So, I remember the difference. You should not expect the battery life of D1 or DX from a 4G phone, at least for now.