From her personal website:
Charles Dickens put it better than I ever could:
'It would concern the reader little, perhaps, to know how sorrowfully the pen is laid down at the close of a two-years' imaginative task; or how an Author feels as if he were dismissing some portion of himself into the shadowy world, when a crowd of the creatures of his brain are going from him for ever.'
To which I can only sigh, try seventeen years, Charles...
I always knew that Harry's story would end with the seventh book, but saying goodbye has been just as hard as I always knew it would be. Even while I'm mourning, though, I feel an incredible sense of achievement. I can hardly believe that I've finally written the ending I've been planning for so many years. I've never felt such a mixture of extreme emotions in my life, never dreamed I could feel simultaneously heartbroken and euphoric.
Some of you have expressed a (much more muted!) mixture of happiness and sadness at the prospect of the last book being published, and that has meant more than I can tell you. If it comes as any consolation, I think that there will be plenty to continue arguing and speculating about, even after 'Deathly Hallows' comes out. So if you're not yet ready to quit the message boards, do not despair...
I'm almost scared to admit this, but one thing has stopped me collapsing in a puddle of misery on the floor. While each of the previous Potter books has strong claims on my affections, 'Deathly Hallows' is my favourite, and that is the most wonderful way to finish the series.