I mentioned this before - the TMP novel is quite interesting is that it suggests that the members of Star Fleet are effectively throwbacks, too savage to be happy on earth.
I have actually always been interested in (and a little scared of) reading this.
I read it when it first came out (dates himself again) and it's been years since I've looked at it. As I recall, it contains references to open, contractual marriages (Kirk was in one with a vice admiral prior to the events of the movie), neo-humans who were very much into group identities rather than individuality, and considerable information (TMI?) regarding Deltan sensuality and their potent pheromones causing some embarassing moments for our stalwart heroes. Sulu, in particular, chose to remain seated at his console at one point.
"Ohh, my."