So now, you can get your phones updated to Jelly Beans (If you haven't got yourself updated yet) with official images.
Official Images also comes handy if you have screwed up your phone by putting in some nasty custom roms.
To Install the factory images there are some small BABY STEPS that you need to take.
I have already posted the method to install the factory image for 4.0 in my previous post which is here : http://abhinavasblog.blogspot.sg/2012/06/installing-custom-rom-on-galaxy-nexus.html
All you need to do is instead of downloading 4.0 OS build you need to download it for 4.1
The entire list of changes in Jelly Beans from ICS is provided here : http://www.android.com/about/jelly-bean/
Happy Jelly Beans... :)