I chose "sometimes" because it depends. If it's a re-issue, a new preface often offers some insight about the "life" of the book since its previous release, etc, or offers a perspective from another person (if not written by the author).
For non-fiction, I usually read it if it seems to contain more than acknowledgements.
For standard fiction fare... well, if it's important it should be in the darn book, not in the preface! It makes me wonder if the book was all done, someone said, "Oh crap, this wasn't explained and doesn't make sense!" so instead of fixing it, they stuck the info in the preface. (They should at least legitimize it by working it into a prologue so it's actually part of the main book text.)
Sometimes the preface is TMI. I was about to read an historical fiction novel that I was really looking forward to. The main character, according to the blurb, was being shunned by pretty much everyone, including her (arranged) husband, because of her inability to bear a child. The big question was, will she overcome this? Will she ever give her husband an heir? Or will she blah blah blah. The preface contained a few bits of info about the locations in the novel, including "The location where Main Character gives birth to the heir is now the site of... "
The author and the editor apparently had never heard of an afterword. Aaargh. That was a long time ago and it still irks me.
|