Do you read forewords/notes that precede many classics? Does it help you or hurt you in your enjoyment/understanding of the work?
Mostly I try to abide by the dictum set forth by Susan Wise Bauer in The Well-Educated Mind: proceed with caution. Forewords may be dangerous, because they often offer an interpretation of a text before you even get to the text. SWB advises--
Do not automatically read the preface. In the case of a nonfiction book, the preface may set the book in context for you...But the preface can also give you an interpretation before you even read the book--something to be avoided...[because it is] something you should do yourself before turning to an expert to do it for you.
Generally, you should read the preface only if it has been written by the author (or translator) personally. If the preface of introduction was written by someone else, skip it. Read the first chapter of the book instead, and if you aren't lost or confused, keep on going; save the reading of the preface until you've finished reading the book itself. If the first chapter befuddles you, go back and read the preface before going on. (p. 43-44)
In this model, you're supposed to be reading the book more than once anyway, so avoiding the preface until after a first read makes sense. Anyway I haven't always got the patience to read a foreword before jumping in.
I mostly do read prefaces of history books. If it's literature, and I'm nervous about the book because I'm thinking it will be difficult, I have been known to skim through it. But I tend to be impatient unless something really catches my attention.