Update 2: meh, I deleted the first update.
Mormons are not christians. They just aren't. Get over it. Matt Stone, Trey Parker, Jon Stewart, most Mormons, etc are incorrect.
I don't see how anyone can read the Book of Mormon (the religious text) and say that it is a form of Christianity by any traditionally accepted understanding of the word from the last several centuries. Beyond a doubt there are a great number of similarities, more so than even between Christianity and Islam (which also uses many of the 'biblical' texts), but the mormon-exclusive teachings are such a radical departure from the general christian theology that it is absurd to say the are the same religion. They are both Abrahamic faiths. They both worship Christ as the Savior. But the differences are even more extreme than those between the major Christian schisms such as Protestantism and Catholicism.
None of this is to say that I think Mormonism is somehow less valid or is undeserving of the same dignified and respectful consideration as Christianity.
I'm an antitheist.
Fuck all religion.
Really though it's depressing that the "are Mormons christians?" issue is such a major one in the US right now. It shouldn't even fucking matter.