Bloomsberg Businessweek (BW) reporter Helen Walters wrote an article on "How Google Got its New Look". Included in the magazine article is a full-page spread on design changes that were made and why. It would make a good poster for any web-design lab or classroom.
I love reading the BW print version over lunch out on the deck, then go online only if there is something special worth sharing. This is worth sharing. Also, the online version includes a short video on how Google evaluates their search page and feedback on its design/redesign.