[Knight of Gondor]

For my part, the movies actually sparked my reading of the books. I'd already read Narnia at a young age, but I don't know how knowledge of Tolkien's books escaped me until the movie scuttlebutt came about.

I quickly immersed myself, and have since become a fan of both.

I think the movies reinvigorated a new generation to be interested, and obviously the interest had other implications. (IE, the Narnia and Harry Potter movies.)

As for their usefulness to the books, I think the movies helped fill out the books. I know there were additions, subtractions and omissions that bothered Tolkien purists, but I immensely enjoyed seeing the events unfold on the screen. I don't think the movies limited the imagination at all. The tenor of the book differs enough from the movie so that, while you can draw comparisons between book and movie, or imagine certain scenes according to Peter Jackson, I can still imagine independently.