I'd like to propose a development documents area on livejournal.org, into which 'transitional' documents go. These are different from the manual in that they will eventually become obsolete and are only kept around for nostalgia/historical reasons. "Introduction to S2" and "Porting LiveJournal Styles to S2" (coming soon!) fall into this category, as they are only relevant during the transition from S1 to S2. Proper documentation will be written later when S2 is all there is, and this will go in the manual.
I only really want this area on livejournal.org so I can put my S2 documents in it for now, since my personal webspace is not the place for it. However, other projects will need transitional or temporary documents in the future.
Since the livejournal.org site lives on Marklar, this could be a logistical problem, but not one with a particularly complex solution as far as I can tell.
So, how about http://www.livejournal.org/devdocs/s2/ ? ;) (This is mostly aimed at Brad, obviously. He'll not see it until he gets back from the Winter Olympics, I guess, but whatever.)