Very little is known about this last entry to Harry Potter's time at Hogwarts except that it will contain the final battle between Harry and Lord Voldemort.
At the end of Harry Potter and the Half-Blood Prince, Harry decides to embark on the quest of finding and destroying Lord Voldemort's remaining Horcruxes. There have been a lot of rumors and "supposed" spoilers, but ultimately no one really knows what will happen or who will die. JK Rowling has stated on her site that she especially wants readers who have grown up with Harry to embark on his last quest without knowing where he is headed.
Some rumors and theories on the net have been corrected by Rowling. For instance, one theory is that at the end of Book 7, Harry and Voldemort will "merge" to form a single persona who can command both the forces of good and evil. Rowling has explicity stated that this event will never happen, seeing that Harry will never wish to be able to command Death Eaters/Demontors/Inferi.
JK Rowling will be doing a huge book signing event on midnight of July 21st, 2007 and will be signing through the night! 1,700 lucky Harry Potter fans will have their books signed by Rowling at the Natural History Museum in London. These fans will receive a free copy of the book, courtesy of Bloomsbury. 500 randomly selected fans will also get the chance to hear Rowling read from the book at midnight.
Furthermore, Bloomsbury has taken extra steps to ensure that Harry Potter and the Deathly Hallows remains unspoiled until the release date. Copies of the book are being sent out to retailers on Tuesday and the trucks carrying these books will be fitted with satellite tracking systems costing up to 1,000 pounds. These systems are designed to make sure the trucks do not deviate from their prescribed route. The books are also on sealed pallets that are fitted with alarms to prevent any tampering. A Bloomsbury spokeperson has also stated that they have a litigation specialist poised 24 hours a day, 7 days a week, to deal with any breaches. They will be enforcing the embargo vigorously and will seek an immediate injunction if required. Experts have estimated the cost of all this at around 10 million pounds, but this is not surprising considering the popularity of the Harry Potter books.
Major cities and bookstores across the world are releasing the book with huge book party launches so be sure to check out the one nearest you!