Interesting detective work and suppositions. I can clear up some of the mysteries, though. (Others are lost in the haze of Everything 0.8.)

• node 0: The 0th node is a virtual node, created on the fly by the Engine. It exists to make locations work, at least in 0.9 and later.
• node 19: The general container changes its parent based on the current user's theme settings. You can't rely on what it says for the parent container, because the act of viewing it can change it. And that's the point.
• node 20: Containers only provide markup (HTML) for content nodes. Nodelets contain HTML and (potentially) embedded Perl code to create HTML.
• nodes 23 and 24: These haven't changed much. The only way to tell what's coming is to crack open nate's skull with a coconut. Or ask him.
• node 84: I believe this is where system default settings live. The semantics have changed in version 0.9. The JavaScript only exists to make it easier arrange elements of a group. Client-side transformation is much faster.
• node 96: Server statistics only shows server date, time, and load. It spawns two shell processes (date and uptime), so it's not too efficient.) Node Statistics shows basic information about the current node, like the number of hits, the nodetype, and the current display page.
• node 106: This is actually the default node displayed when users don't request a node by id or name. The administrator can change the system default node in the system settings -- it now points to The Monastery Gates. The ultimate parent of all nodes is node, probably node_id 1 or 2.
• node 107: I think nate wrote this. It's out of date. The manual is more complete.
• node 110: Each user sees personal settings here.
• node 111: The date is probably the release date of the Engine vroom used to set things up.
• node 114: As they say on Everything 2, these are owners/employees of EDC, and only have this access to see how things are done or to fix things when vroom is passed out after a long night of studying.
• node 126: I've heard that these things happen. Two tests are better than one.

For more information, see the 'manual' link above, or download the latest version yourself and play with things.