"It’s a common and easy enough distinction, this separation of books into those we read because we want to and those we read because we have to, and it serves as a useful marketing trope for publishers, especially when they are trying to get readers to take this book rather than that one to the beach. But it’s a flawed and pernicious division. This linking of pleasure and guilt is intended as an enticement, not as an admonition: reading for guilty pleasure is like letting one’s diet slide for a day—naughty but relatively harmless. The distinction partakes of a debased cultural Puritanism, which insists that the only fun to be had with a book is the frivolous kind, or that it’s necessarily a pleasure to read something accessible and easy. Associating pleasure and guilt in this way presumes an anterior, scolding authority—one which insists that reading must be work."
But of course, most of the time it isn't. This is from a fine New Yorker piece by Rebecca Mead, who wrote a splendid book about reading Middlemarch. You can find it at http://www.newyorker.com/culture/cultural-comment/pleasure-of-reading
I was thinking about this distinction at the book fair today. There were scores of copies of recent mass market best sellers, from Philippa Gregory to Stephen King, but there were also plenty of copies of the "classics" of every era - books that people have so consistently responded to that they have embedded themselves in the life of readers in English everywhere.