I think we all expected this, since the Galaxy Nexi that were handed out to attendees at Google I/O had Jelly Bean on them, it was only a matter of time until this build made its way to other Galaxy Nexi out in the world.
So a number of developers around the net have gotten this working for you and it doesn't matter whether or not you're on a GSM Galaxy Nexus or the Verizon variant. If you're rocking a GSM Nexus then you want to head over to XDA here, where a productive fellow by the name of PTZero is to thank for this. If you're on Verizon then you're going to want to go to RootzWiki here, where a fellow by the name of jdkoreclipse is to thank for this. Oh, and did I mention that LTE now works with that last one?
If you're rocking a Nexus S still, like this poor editor is there are a number of folk over at XDA that are in the process of porting it from the Galaxy Nexus and they appear to be getting closer and closer as we speak. I'll be sure to snap that up and try it out on my phone straight away so, stay tuned for Nexus S news of sweet Jelly Beans.