The Church's media relation director, Michael Otterson, has a blog on the the Washington Post's On Faith site. His post today reiterates the proper use of the term Mormon, and includes a link to a Reuters article and his own video statement. Backtracking to the Church's Newsroom site (http://newsroom.lds.org), you can find this video along with a video of President Hinckley, the president of the Church who passed away earlier this year, "speaking about the clear distinction between the Church and polygmagous sects."
On a related note, I've noticed that many journalists are referring to the polygamist groups as fundamentalist Mormons. Despite the F in FLDS standing for fundamentalist, these groups are not fundamentalist in the sense of following the fundamental tenets of Mormonism. Just because they've named themselves that doesn't mean that they are.