A thought that's just struck me, sighing over the insane tab jungle in my browser and the feeling of unutterable loss that comes over me when I close even one.
and wondering why bookmarks don't substitute for tabs?
And it hit me:
Tabs are our Memex trails!
The back-arrow stack on each tab stores vital context information on 'what does this page mean to me, what does it relate to, what search was it part of, what is its provenance...'
This is Memex data! *AND BROWSERS DON'T KNOW ABOUT IT*.