From Publishers website:
The purpose of this booklet is not to provide a comprehensive list of everything that has changed with the 3.5 revision. The changes are too large in number and varied in scope to be able to provide an all-inclusive inventory. Instead, what we want to do is to show you a broad picture of what has changed and to provide you with support for updating our most popular product.
Do you need to make these changes? No.
This booklet is for players and Dungeon Master who value rules precision and need to know what's changed so that they can continue to enjoy their 3rd Edition producs.
You might choose to make notations in your existing books, photocopy and cut up this booklet to add bookmarklike inserts to your books, or simply use this booklet simultaneously with your books.
We provide a brief general overview of the core books and detailed revision nots for Deities and Demigods, Epic Level Handbook, Fiend Folio, Manual of the Planes, and Monster Manual II.