DVD vs. Book
DVDs are for individuals who are visual learners. Most DVDs contain anywhere from 4-12 different effects and are taught from several angles and distances by a [hopefully] effective teacher. Some people find this way the easiest to learn, and DVDs are also good if you're having trouble learning something from a book
Books, on the the other hand [which I prefer] can contain dozens of times as much effects as a single DVD. Books may include illustrations, but most all magic books have comprehensive text. If you take a second to get used to the writing style of the author and understand the vocabulary, you will quickly find a way to take advantage of the incredibly encyclopedic resource books can be.
DVDS:
.: Visual
.: In-depth
.: Solve issues you may have with certain sleights
.: Can be copied, saved, more portable
Books:
.: Cheaper
.: Contain many, many effects
.: Something for EVERYONE in any book
.: Incredible resource
Take into account your situational needs when deciding what to purchase.
To compare, I have reviewed my DVD for Alex Lourido's Butter coin [Pengiun Magic.com] and the 1981 edition of J.J. Bobo's Modern Coin magic [Borders]
The DVD was about $30, and comes with six effects. The teaching is mediocre but it is nice to be able to see exactly how to move my hands when handling the coin. With the DVD, angles, handling, and setup are not an option. By watching the DVD once, I was able to soak in the six mini-routines and get a sense for how to perform with the coin.
Bobo's Modern Coin Magic contains hundreds of sleights organized by type, plus 18 full routines. It was $10. The illustrations are mediocre, but there seems to be an illustration for every single potential issue. I had occasional problems understanding exactly what the author meant in regards to handling, angles, or subtleties, but after reading over a few times while playing with a coin, I comprehended the sleight.
All in all, I think the book is a vastly superior resource for anyone who is remotely serious about becoming a performer.