Drupal under-the-hood

I have a growing urge to start hacking my drupal-backed site gandrew.com. Partly I want to improve my current website, secondly I intend to start work building my dream personal publishing system soon.
Before starting, I wanted to get a really good overview of how drupal works beneath the hood; fortunately there are some excellent articles written on this very topic

• Walkthrough of Drupal's page serving mechanism - Start here.
• Drupal menu system reference - "The Drupal menu system drives both the navigation system from a user perspective and the callback system that Drupal uses to respond to URLs passed from the browser. For this reason, a good understanding of the menu system is fundamental to the creation of complex modules." - Couldn't say it any better.
• Walkthrough of menu-building mechanism - This walkthrough follows on from the page-serving walkthrough, but is a little less clear, which is why I recommend reading the reference first.
• Walkthrough of node-building mechanism - The next step in the page building story. You might also want to look at the source of a few node types (especially the implementation of hook_load() )
• Theme Developer's guide - The theme system is the last part of the page-building story unfortunately there isn't a walkthrough (maybe I should write one?), but this guide is fairly thorough.

You will also want to have the Drupal API reference handy, as well as having some useful reference you can also access a nice pretty printed view of the source which you can read while following the walkthrough.