I have read all the Carlos Castaneda's books, I practiced some of their exercises, some have been helpful but I've always been in doubt about whether Don Juan ever existed, or if the events in the books from Carlos Castaneda never happened.
About the author from Wikipedia:
Starting with The Teachings of Don Juan in 1968, Castaneda wrote a series of books that describe his training in shamanism. The books, narrated in the first person, relate his experiences under the tutelage of a Yaqui "Man of Knowledge" named don Juan Matus.