From STAR TREK: THE LOST BOOKS:
There are at least fifty changes from the first version to the revised version, some as short as a single word, others as long as a paragraph or two. Most of the excisions involve scenes in which there is physical contact between Kirk and Spock (for example, describing the warmth of Spock's hand on Kirk's face during a mindmeld). But there was also a sentence that described Spock's realization that Kirk was the person Spock was meant to spend his life with.
Copies of the original can still be found in used bookstores and at conventions, so this book isn't completely lost yet. If the cover has raised letters for the title, it's likely to be the original; if not, check anyway, because at least some copies without raised lettering have the unexpurgated text. Better yet, just check page 41 for a passage that begins, "I understand that you were probably playing with dolls and wearing lipstick until you were twenty!" That appears only in the original.
So, there ya go -- these are little-known facts that now, you know!