Well, we now have yet another reason to envy Google I/O attendees - a signed copy of the official Jelly Bean build has just been released on the 'nets, but it seems to only be working on the 'takju' (GSM) Galaxy Nexuses given out at I/O 2012 (or at least those GNs with the IMM30D firmware).
You can grab it for yourself right here, if you're interested in what's inside the 156MB ZIP. Don't worry, GN owners - we're sure with the appropriate modifications from the dev community, you'll be able to flash some version of this soon enough - not to mention the countless other goodies that might emerge. The real question is when this will be ported to other devices. And now we wait.