Just in the process of downloading an update for the Lumia 800 but can’t find out what the update does but I am assuming this is the improved battery performance. Will let you know how it goes.
Update 1: Have run the phone for a day now and cant say I have noticed any difference, I would say I am a heavy user at times, with emails set to check every minute, wireless always enabled, twitter, location services running and the screen on full brightness.
So for me at the moment the jury is out, I am lucky in that when I am in the car or at work I will normally keen the phone charging, its when thats not a option it will be more noticable. With another update in the pipeline for next month we will see what difference that makes……….if any.
Update 2: I have noticed that the brightness of the screen is more responsive to your environment, when I first got the phone and I accessed the phone in the dark it glared at you, now it will increase or decrease based on your surroundings.