Have you unlocked and rooted your Android phone?
I bought the Verizon Galaxy Nexus on release day back in December, and have enjoyed stock ICS since then. Now with the release of Jelly Bean and Verizon's poor record in releasing updated (they'll get 'em out, but months after everyone else), I've decided to unlock and root, then flash a JellyBean ROM. Frankly, I had to do a factory reset to fix some other issues, so since I'm starting with a blank slate seemed like a good time to try.
I'm using Wug's Galaxy Nexus Root Toolkit which seems to be making it (relatively) idiot proof. Unlocked yesterday. Rooted it today. Currently doing a CWM backup, then will try flashing the Toro Jelly Bean ROM. Any tips/tricks/etc I should be aware of from people who've done this before?