Depends. Sometimes the intros to books require you to be intimitely aware of the stuff going on in the book, making it worthless for someone who hasn't read the book to read it. I have a volume of Keats' poetry and I started reading the intro and realized that not only did the intro require a knowledge of Keats and his Poems, but also required a deep knowledge of the art of Poetry itself. I naturally had to skip that one because they were going into concepts that were far beyond where my head was at (I just wanted to read some poems from Keats!) The only way to really tell whether or not an intro is worth reading, funnily enough, is by reading it. Usually a few pages should let you know whether it's an intro like the one above or an intro that anyone new to the book could read. So, it's back to: depends.