A short 10 days after my Google-icious post, Google has implemented the idea, with nary a nod in my direction. Isn't 10 days just enough time for someone to read my post, organize a project team, develop the feature, test and debug it, and release it to the public?
In any case, it's clear that someone at Google thinks that merging bookmarking with search is a natural idea. The implementation is not perfect (bookmarking is buried within Google's Search History which I've never actually used until today), but the feature's presence is a good sign.
* float bookmarks up to the main results page (possibly the plan after beta)
* default the Labels field to the search terms used in finding the item
* just call them Tags already!
* not sure if I like having to click twice to add "Labels"
* add "remove" links for both bookmarked and unbookmarked history results