I haven't been on these forums in a while, admittedly, but glancing through some threads it seems there are quite a few people who don't have Jelly Bean on a rooted Nexus yet. I'm pretty shocked, as I've had Jelly Bean for weeks now, so I'll give you a litle review.
Remember the difference between ICS and the previous version? Well, that is a drop in the bucket compared to Jelly Bean. Jelly Bean has made my Nexus a perfect phone. When I say perfect, I mean perfect. This is the best I've ever had any of my phones ever run. It's ridiculously fast/fluid compared to anything before it. Battery life is great. No force closes, no bugs, no problems. The phone just runs great and feels great. When the s3 came out I was somewhat tempted to go out and buy it, then Jelly Bean came out. So, I installed it and all my feelings of getting an s3, the "latest and greatest phone" just went away. I have no desire to upgrade, I don't even have a desire to update anymore. There is no reason to - I can't improve performance at this point. Maybe there will be a new feature or two in the custom roms I may want, and I may update to a new version, but there is absolutely no rush.
I can't recommend it enough. The difference is vast. I couldn't even think of going back to ICS at this point. Jelly Bean, and Franco's Kernel 240 are really THAT good.
Anyway, I'm not going to write a guide or instruct how to root or any of that, as I'm sure there are tons of those types of posts out there. I will provide some links to help you guys get started. Trust me, you have no idea what you are missing. If you have ICS, I actually feel bad for you. It's THAT much of a difference.
Here's my personal favorite ROM, the one I've had no issues/bugs/problems with, Xenon :
[ROM][JB] XenonHD vX (25.08.12) *ProjectX* - [VZW] Galaxy Nexus Development - RootzWiki
Here's a list of different ROMs, if you want to choose:
[VZW] Galaxy Nexus Development - RootzWiki
Franco's Kernel, I use r240 512 and no issues, but some have. Just use the 384, as it should work on every phone. Battery life/speed is *great*:
Index of /franciscofranco/Galaxy Nexus/JB/Jelly Bean
Anyway, good luck. Root. It's simple, and it's amazing.