This review of ZygorS 1 TO 70 Leveling Guide supplies some nice links to other sites and articles that review the guide.
The site also gives a review. Basically giving it a huge thumbs up of it's own. It outlines the some of the drawbacks that hinder peoples attempts to power level 1 to 70 and then explains how Zygor Guides address's these stumbling blocks.
One of the factors that the review focus's on is the fact that so many people have to alt-tab out of the game to aquire the answers to they're questions. Meaning that a huge chunk of game time is wasted. This is where a power leveler and your average joe player differs.
The power leveler spends every ounce of his play time in game and this is where Zygors 1 to 70 alliance and horde leveling guide, out shines the other guides. It is totally in game, meaning that you have a step by step guide that automatically guides you at every step, meaning that you no longer have to leave WOW running as you search for your quests and more et