How difficult would it be to add a private note feature to question pages? It would be interesting if one wants to make notes for work products on a page or implementation specifics without exposing those to the public.
A completely off the wall suggestion:
Rather than use Firefox / Chrome / whatever to keep your notes organised, because let's face it, browsers are rubbish for this sort of thing (I always feel scrapbook is ok but not great for seriously lengthy notes, why not install Greasemonkey and then add this script which adds a handy link to Stackprinter.com. You can then produce a dead tree copy, if you so like, or do what I do and use CUPS-PDF as the printer to archive questions I like. If you so wanted to, you could add pages to that pdf using one of the variety of scripts out there for your notes.
Of course, there is always the problem of the "moving target" that questions/knowledge become obsolete/superceded/updated very quickly, but such is the nature of anything.