As tight as the Blizzard team claims it is, and as much as it professes to act only in the best interest of gameplay, this promotion may have been poorly conceived. It seems like the Marketing Department had a great idea to accomplish two goals: (1) acquire more accountholders and (2) encourage current accountholders to stay. However, I wonder how well this idea was vetted by the game design team. My guess is: not well at all.
The point of leveling -- at least the way WoW was originally designed, although maybe not so much lately -- is to teach the player how to use class skills. You get spells and talents over time, along with the chance to practice them before you learn more new spells. What happens if you level too quickly? The same thing that happened to me as a Death Knight: you end up having no idea what you're doing, mashing random buttons and crossing your fingers. Pugging instances is hard enough as it is without having to teach level 59 players how to use their spells or wasting all your mana healing them because their gear is too low. Although the Recruit-A-Friend promotion was likely a business response by Blizzard to allay some of the ennui (and ensuing account closures) that has arisen in advance of the Wrath expansion, I wonder how much (not if) it will hurt the game. Perhaps they have the metrics to suggest that a promotion of this type will hold enough borderline accounts to combat churn, but I'm not sure if they anticipated counter-churn, which is what happens when customers leave as a result of players acquired by the promotion.