DW pros:
He's got phenomenal timing and a LOT of (probably unconcious) physical presence that he uses to control (or dominate, depending on how you feel about this method of control) dogs. He's also a marketing GENIUS, and has phenomenal timing for applying corrections (or praise/treats, for that matter.)
Cons: 99.999% of dog owners (and trainers) cannot replicate these traits.
Timing is essential in ANY training method- if your dog doesn't get the feedback ("what you just did was good/bad") with appropriate timing, you'll have a VERY hard time training him/her. Period. So there's going to be a learning curve with ANY training method while you get the mechanical skills down to reward (or punish) with appropriate timing. HOWEVER - if you're using positive methods, you're a lot less likely to damage your relationship with the dog (or the dog himself!) with poorly timed rewards.
His books are very poorly written, IMO (to be fair, I suspect they're ghost written) and really shouldn't be marketed as training books so much as 'how to think about your dog' books. (For example, "The Other End Of The Leash", which I recommended above, recommends only a very few specific exercises to work on with your dog, which is why I haven't listed it as a training book. The DW books are in this same catagory, but with less science and more marketing.)
A couple of quick links:
http://4pawsu.com/dogpsychology.htm
http://4pawsu.com/cesarfans.htm