One of the reasons I love Nexus devices is that Google itself takes care of updates. Another advantage is access to factory images which allows me to go back to 'as I bought it' condition.
These images not only allows current Jelly Bean users to restore their phones but also allows other users who are still waiting for Jelly Bean on their Nexus devices to upgrade with greater ease.
You can check out the images for your device on this page. Google has, as usual, also published detailed instructions on how to use these images.