Dad of a Mormon wrote:
I have read it. I'm interested in your answer to the question. Do Mormons believe that God was once a man?
Though you didn't ask me this question, I will answer with a qualified "yes."
Pretty much anybody who knows anything about the King Follett Discourse (as well as the subsquent Sermon at the Grove) believes that God was once a man.
There are lots of members, though, who really don't study much on their own, and just go to church and listen to what is taught there. Because this concept really is not much taught in the thoroughly correlated church meetings, it is quite possible for a person to go to church their whole life and never encounter this teaching.
I have encountered members who have taken this teaching and applied it to Christ, saying that God (i.e., Christ) did live as a man (on this earth). This strikes me as a popular reimagining of what Joseph Smith was teaching that keeps Mormons within the Christian mainstream. More troulbing are those Mormons who will give this explanation to non-members while privately understanding Joseph Smith meant something different. I have encountered such Mormons. I may have been one at one point.
I think it is clear that this is not what Joseph Smith was talking about, but I could be wrong.
What makes it more difficult is that we don't have the actual words Joseph Smith said. It was a funeral sermon he gave in Nauvoo in 1844 shortly before his death, and there were about four or five gentlemen in the audience who took notes on what Joseph Smith said. They are shorthand in nature and can be found in their original form in a book called The Words of Joseph Smith.
(I think this may have been the basis for some of President Hinckley's equivocation on the issue. It might have been better for him to explain what he meant, but then, he also knew he didn't have time to go into a historical treatise on the subject.)
More common is for Mormons who know anything about the King Follett Discourse to have encountered it in a different book called Teachings of the Prophet Joseph Smith, in which the different shorthand accounts were cobbled together into one long sermon.
If memory serves, none of the shorthand accounts contradict the idea that God was once a man, and most if not all mention it. It therefore seems almost indisputable that this is indeed what Joseph Smith taught.
For myself, I do believe it as a theological principle, that God was once a man as we are now.
But I could be wrong . . .
The couplet referred to by President Hinckley was not stated by Joseph Smith, but by an apostle at the time named Wilford Woodruff, who subsequently became the fourth president of the LDS Church and was one of the gentlemen who took copious notes of Joseph Smith's King Follett Discourse.
If memory serves, Wilford Woodruff said this concept came to him as if by revelation, but he kept it to himself because he considered it so radical. Wilford later reported he went to Joseph and presented the couplet to Joseph Smith, at which point Joseph Smith confirmed it was true and a revelation from heaven to Wilford Woodruff.
All the Best!
--Consiglieri