Cool. I had no idea...

Finally, I've found somebody who spells out what all of these mysterious (to me) Windows "toolkits" and "upgraders" etc.. are actually doing. Here's the step-by-step guide for doing it in a simple, driver-free way, from the command line (on Linux, but should also work from OS/X or WinXX):

http://www.cvr.cc/jelly-bean-on-your-galaxy-nexus-phone/

FYI, there's a leak of the Verizon Galaxy Nexus Jelly Bean update. You can find instructions here.

My primary desktop is packed away (we're trying to move), so I had to learn how to unroot, flash, root, etc on my MacBook. That was an interesting experience. As you might imagine, there isn't much information out there for Mac users on Android rooting/roming, but I was able to patch enough together to get it done, and in the end it was actually pretty easy. It was certainly the most time I've spent in the Terminal so far