The answer to your question depends on how one defines the word cult. I am looking at my Webster’s and it defines a cult as "a system of religious worship or ritual." By this definition, true Christianity is a cult, and so is mainstream Mormonism. I assume that when you are asking whether Mormonism is a cult, you are assuming a much more negative connotation of the word cult. Let me give a definition of the word cult as I believe it is used in a negative sense in the US today. A cult is a religious group which is headed by a living authoritative figure who controls major aspects of the lives of the followers such as their finances, living situation and employment. By this definition, Scientology works as a cult for many of its followers. Also, Catholic and Orthodox monasteries function as cults.
As for Mormonism, I believe that the Mormon movement in the mid-1800’s met this definition of a cult. Both Joseph Smith and Brigham Young met the classic negative definition of the cult leader. They were highly charismatic leaders who expected total devotion from their followers–to the point that members gave up their livelihood and moved to follow the movement. Also, the Fundamentalist Latter Day Saints–a splinter group which split from Salt Lake City Mormonism about one hundred years ago definitely is a cult. They practice polygamy, use exclusion as a weapon to enforce conformity and live in exclusive communities. However, I believe that the definition I have given above for a religious cult does NOT apply to mainstream Mormonism today. Bottom line, despite some really wierd practices (from our perspective as Christians) such as the wearing of odd undergarments and the rather strange ceremonies surrounding temple worship, Mormonism has moved from a cult to a religion.
Perhaps what you are really asking is whether this group is Christian. Some Christian apologists label any group which is pseudo-Christian but which does not accept the orthodox view of Jesus as a cult. Using this sledge-hammer approach, they will label Jehovah’s Witness and Mormonism as a cult. I believe this is not a careful use of vocabulary. By this definition Islam, Buddhism and Hinduism are cults. Of course they are cults by the Webster’s definition I mentioned above, but then probably the group you are a part of is a cult as well by that definition. The word cult should not be used as a weapon as such a weapon can be turned back on the one who uses it. I believe that Mormons are not Christian because their view of Jesus is a radical departure from the biblical view, but I would prefer not to use the word cult indiscriminately on this group.
I hope this general description will help