Been running JB since I got the phone- CleanROM 5.0. Stable, great battery life, Touchwiz JB complete with Google Now awesomeness. The problem is that we have to wait for Verizon to have a leak, and that means the actually has to BE a leak. I'm not anticipating having much support for our phones from here on out. After JB, the party may be over. The support on my Thunderbolt was absolute balls- it took months and months for it to get Gingerbread (thats right, it was running Froyo!!!) then that was the last OS update we received. The ICS update was promised, but never came and devs had to build a cracked verison of ICS they best they could from a buggy leak by VZ. Maybe the fact that the S3 is released on multiple carriers in identical form will give us a better chance at getting updates? Who knows.
I'm guessing this will be my last VZ phone anyway- I'm incredibly tired of dealing with the lack of support and once they finally take my unlimited data away (which I'm predicting is coming for us all) I will buy a Play Store Nexus and that will be it. If you want the latest OS, you'll have to do it the hard(er) way- go to XDA, follow Adam Outler's root guide, root-unlock-*backup*-flash CleanROM or a rom of your choosing and be done with it.