The reasons for the delay in churning out the fifth book in the series: Lack of time. The Harry Potter film, a North American book tour and other projects have stolen Rowling's writing time. Chief amoung these projects are two Harry Potter companion books Rowling is writing for a U.K. charity called Comic Relief. The books, "Quidditch Through the Ages" and "Fantastic Beasts and Where to Find Them", will appear under the pseudonyms of Kennilworthy Whisp and Newt Scamander on March 12. Rowling will donate net proceeds to the Harry Potter Fund at Comic Relief, U.K., a charity set up to help children in developing countries.
Still, given that book No. 4, "Harry Potter and the Goblet of Fire," checks in at a sturdy 734 pages, the delay might give everyone a chance to finish that one before springing for the next.