This afternoon, I found an intriguing article by John Granger, author of The Hidden Key to Harry Potter and Finding God in Harry Potter (the latter I haven't gotten to read yet, but would highly recommend just the same). He received top prize for "The Alchemist's Tale" at the Nimbus 2003 symposium on Harry Potter last July.
Basically, the article is a summary of his books' major premise, which supplies an answer to both those who condemn the Harry Potter books as "lowbrow children's fiction" as well as those Christians who decry the series as promoting evil and witchcraft. He contends that J.K. Rowling draws much of her theme and source material from the tradition of Christian literary alchemists (which he explains in this article). I am even more convinced from Granger and others that Rowling is a Christian, writing with medieval themes in mind.
Because of this, I anticipate the sixth book that much more, holding fast to my conjecture that Albus Dumbledore is, or is closely related to, the Half-Blood Prince-- somewhere along the royal line of Godric Griffindor. What did ever happen to Dumbledore's brother, anyway?