Seth Godin writes about the long trail at his blog today. In marketing books, you have to look to the long trail -- what happens three or four years after the book is published. For self-publishers, especially, it's important to take a long-term view when marketing your books.
In his blog, Seth mentions the success of The Shawshank Redemption after its movie run. It's one of my favorite movies, one of those that makes a great DVD buy because it's worth seeing more than once.