DVD's have their place indeed. My personal opinion is that DVD's should only be for things that are incredibly difficult to put into print, or that are "must see" things. For example, I love being able to see Ray Kosby do his card magic. Although his material could be put into print, it is particularly great to see him do it. I would love to see Earnest Earick also put out a "By Forces Unseen" DVD just to see him do it (which he can from what I hear).
A DVD should have a great quantity of material, almost equal to a book impossible. John Bannon has released some of the best DVD's that I've seen in years. His Bullets After Dark and Bullet Party are fantastic, full of USEFUL information, and such a great time. One-trick DVD's shouldn't exist in my opinion, or should include way more thoughts, philosophy, and technique into them. A single DVD isn't really making you grow as a magician, instead only adds to your repertoire. The test of fire: Will it become a classic?
If the answer is "no", and the DVD is becoming something that will be buried under all the new products after it,then was it worth releasing? Personally, I wouldn't. I aim at releasing classics of magic, not one-hit wonders. Then again I don't plan on releasing any more magic anytime soon either, mainly because of this point
Books follow the same rules in my opinion, except that they have a higher criteria. If a book is full of junk, that's a lot of junk to write! Believe me, there have been some books published recently that are junk, but it's a safer bet that it won't be versus DVD's.
My beef with the markets today, and the way magicians learn, is that they take DVD's as their core source of learning. The occasional DVD candy is ok, but when it's your main source then you have a problem. I myself purchased Jack Carpenter's Super Session DVD's. They turned out to be a great watch as I felt like I was hanging out "with the guys", and it's a nice thing. However, rest assured that I purchased three books along with that DVD!