I did read the JLS when I was preparing for the SCJP. I have to admit that it is not absolutely necessary to read it in order to pass the exam or get a good grade. You could use the JLS, if you want, as reference book.
However, I have to say, also, that reading the JLS helped me understand many of the SCJP topics even better than before reading it. Many of the examples that come with it are very revealing and most of the times helped me realize of thing I had probably overlooked when studying for the exam.
All been said, I would say that reading the JLS might increment your understanding of the
Java Programming Language regardless of this further comprehension is useful to pass the exam or not.
[ May 24, 2006: Message edited by: Edwin Dalorzo ]