Castaneda appealed to all types of believers, including those who were too rational for new age. Whether or not you believed he actually met with a Shaman and saw through to the source of all things, much was still valuable regarding the way of life he preached. Much like any other belief system, it's easy to pick and choose great teachings from his works. (You may not belief Christ rose from the tomb, but it's difficult to argue with "treat your neighbor as you would like to be treated.) This pulled in a great number of people and Castaneda was dubbed the Godfather of New Age.
In addition to the appeal of the masses, Carlos drew in academics and intellectuals with what seemed to be a knack for narrative anthropology. Because he was simply engaging in the rituals of the Native Americans, it seemed more that he was studying a culture, and his books were taken as real anthropology. His books have generally been accepted as non-fiction throughout the years. In 1972, a great deal of skepticism led to the debunking of most of Castaneda's lies, and he disappeared from public in 1973. It's what happened after this point that drains the humor from the situation.
Castaneda began a movement known as Tensegrity, and had many devoted women followers known as witches that included past and current lovers. They lived in secrecy, separated from theif families, used numerous aliases, and didn't allow photographs.
Castaneda definitely has moved New Age from funny to Creepy as hell in my book. I've got the creepy shivers. Think I'll go look at some cuteness and shake it off.