Will You Read/Review/Write About My Book?

Every week I receive a number of manuscripts, books, and email attachments from authors requesting that I read the material and provide them with a review or other comments.  I receive many more emails simply asking if I would be willing to read and review a manuscript if it was sent my way.  Some of these materials come direct from publishers; the rest are sent by the author personally.  Nearly all of them are posted politely and without onus, but I get guilt pangs anyway, because, A) guilt ...