Which method?
I ended up using Paul O'brien's Superboot method. It's one of the ones linked here:
http://androidforums.com/galaxy-nexus-all-things-root/452146-how-root-samsung-galaxy-nexus.html
The catch (for me, anyway) was realizing that there is no visible indication of success. The phone boots to a Google logo and just sits there. Apparently, at that point you're done. Took seconds.