With King, I read the introductions. With other books I'll start and it just depends if I feel like it's pointless or not (sometimes they can be rather dry). If not, I'll skip it and start the story and go back and finish it later. It doesn't bother me if someone doesn't read them. Who cares, their loss.
Love em, love em--intros and afterwords. Sometimes King's intros are better than the book. Heh.
BUT...beware of intros to older books, back before the concept of 'spoiler' was invented. Case in point; the other day, I read John Chamberlain's intro to the Modern Library omnibus of James Farrell's Studs Lonigan trilogy, and he totally gives away the ending and several key plot points. Man, that burned my bisquits. I've noticed this happening in many intros to classic books, so if it's an oldie, I skip the intro till later.
With King's books -I ALWAYS read the introduction and afterwards. In fact, I'm so disappointed when there is no intro that I feel a bit cheated (as if an 800 page book isn't enough!)...I love, love, love some of King's intros in his earlier books. The one that has always stuck in my mind is when he talks about not putting his hand over the edge of the bed!