JK Rowling, author of the Harry Potter series, recently gave a commencement address at Harvard University and was awarded an honourary doctor of letters degree.
This is an excellent read, and gives great insight into the books. Of course, I was also happy to read that she was a Classics major (as was I). What was truly enlightening regarding the books, though, was her recounting of her experiences while working for Amnesty International. I'd say that those experiences very clearly informed the darkness present in the books.
Two themes she addresses very well are the importance of failure, and the importance and power of imagination. I strongly recommend reading this commencement address, whether you're a Harry Potter fan or would simply enjoy an insightful essay.
Addendum: Here's the video.