News: Jelly Bean Factory Images Released for Galaxy Nexus, Nexus S, and Nexus 7
Google has released the official Android 4.1 factory images for a handful of Nexus devices. The company posted the factory images for the Nexus 7, Galaxy Nexus, and Nexus S on its developers blog. Keep in mind that the CDMA variants of the Nexus S and Galaxy Nexus are nor supported at the moment.
These files should make device modifications quite a bit easier and less stressful, as you can roll back to a factory image. You can head over to the Google Developers blog to download the files for yourself.