http://originaltrilogy.com/forum/topic.cfm/STAR-WARS-Movies-Animated/post/402894/#TopicPost402894

This conversation (for me) is spiritually living on here.

Here's an excerpt:

Perhaps the human clones "don't work" because they "have no mind." Their bodies are completely functional, but their brains just don't work. They simply lie as if in a coma. But Palpatine, seeking immortality through manipulations of the Dark Side, is also using the clones- not to build an army, but to create an infinite supply of Palpatine bodies which he can use to transfer his dark soul into. So this gives Palpatine a motivation for the prequels besides simply "conquer the known galaxy." But, probably best, in my opinion, it gives you a reason that Vader would server Palpatine and the Dark Side. If transferring your soul is one of the hardest "spells" in Dark Side Magic and Vader has to learn it from Palpatine and also gain proficiency at using the Dark Side... well, it sure beats the "Join me and the Dark Side so that your wife can live forever. By the way, she's dead and you killed her, but joine me anyway." logic of Revenge of the Sith.