Please post your experience post GDR2/Amber update.
I'm currently running GDR2/Amber on my unbranded Lumia 920 for the past two days and here is my short experience:
* Battery life has been amazing for me. It has improved by atleast 30% for me. (Phone easily lasts for 24 hours with crappy 3G signal) I had a very crappy battery and Nokia refused to replace my handset.
* OS seems a lot more snappy but this could be placebo
* I love Nokia glance screen. I wish it could show notifications too and not just time and battery
* I have got Data Sense in this update which is awesome. No more worrying about exceeding my mobile data.
* There used to be this weird bug where increase/decrease of volume basically had no effect while listening to music, this seems to have been fixed.
* Nokia Pro cam is awesome and is my default camera now.
* Used to get this random error on Xbox Music wherein the song wouldn't play. I think this update fixes that bug too.