Readers of this site will know that I have a very high regard for the tutorials produced by George Jardine. His series discussing the Lightroom Library and Develop modules are already linked from early posts.
Recently while I was in the US George dropped me an email to let me know that he had updated his tutorial describing how the Highlight and Shadow controls in Lightroom 4 and Camera Raw 7 work, and would shortly be publishing a video tutorial. The tutorial has been available for a while now, but the video has just gone live.