I have had hours of pleasure reading and re-reading certain books, the one that stands out for the last few years have been Harry Potter. So have countless others. (In fact I just finished re-reading Harry Potter and The Prisoner of Azkaban. A quick weekend read)
I think the best way to repay Rowling (ok! she has become rich and all that but ...) would be to have a platform 9-3/4 at the Kings Cross station in London.
Note: The picture used here belongs to G Schouten de Jel. Visit his gallery to see more such photographs.
