I love the series and just started the book. I cannot imagine how anyone can understand what is going on in the series without reading the book at the same time, but I think HBO has done a brilliant job with it nonetheless.

George Martin keeps everyone abreast of updates (books and show) on his comm grrm. Rest assured -- he has the whole series planned out, even if they aren't written. You have to think of it in terms of Harry Potter - JKR wrote the last chapter before she wrote the other six books.