Dean's World has a good article on what traits distance a cult from an established religion. Touches on Scientology and Islamofascism. It's true that by definition a major world relgion can fall under the category of "cult," but the word clearly has negative connotations, and is more commonly used by the first definition listed at Dictionary.com: "A religion or religious sect generally considered to be extremist or false, with its followers often living in an unconventional manner under the guidance of an authoritarian, charismatic leader."