I updated my 820 via NSU for retail (India)
(Vodafone user btw)
These are the changes I got :
1.Storage Check in settings
2.Data Sense
3.I am getting HSPA+ signal on 3G mode
4.Scrubbing response on HD videos has improved a lot
5.Music Player is little fast
Problems :
None so far , Apps are getting updates , able to install apps through SD-card , backing up is fine , camera works fine.Everything is very nice.
Most importantly no bugs.
EDIT : For those who want to update , here's the installation software :
http://www.mediafire.com/?xfpzsda55rqy7e7
Data will be wiped and u can easily restore it when phone restarts after update