He Wants to Create 'Book Summary' Business

I have an idea for a book summary business similar to the business book summary sites around the web, but I want to make sure I'm clear about the legality before I begin. In short, do I need permission from the copyright holder to create these summaries for sale? This is assuming that the summaries would be in my own words as much as possible and little to no direct quotations if needed. If it is your own expression and you're not quoting from the text, you should be fine. What can land you in hot water is extensive use of excerpts (or serious paraphrasing) and similar "copying" behavior as outlined in these literary fair use cases. BTW, here's an example of a lengthy, non-infringing summary, of one of our favorite new books.