One thing I caught long ago is something not many people seem to have noticed. That being the connections between Demolition Man and Brave New World by Aldous Huxley.
I wouldn't go so far as to say the movie was based on the book, but it certainly borrows quite a few elements. It has been awhile since I read the book, so bear with me. First and foremost, there's the matter of the revamped, dystopic "society of the future", overflowing with a nauseating amount of political-correctness, and a total lack of extended inter-personal relationships (unlike the book, however, sexuality - even physical contact is almost totally eliminated in the movie, however both the book and movie share the idea of procreation being carried out in a lab). Then of course, there is the unruly group of "savages", outside the reach of the general populace. In the movie, they live underground, while in the book they're placed in reservation-like areas.
More into the specifics, we have someone from the new society (Sandra Bullock's character) befriending someone from the savage society, that of Stallone's character. Even the names of the characters allude to the book. "Lenina Huxley" is a combination of "Lenina Crowne" from the book, and "Aldous Huxley", the author. Then there's the fish-out-of-water character of John Spartan, who doesn't fit into the new society very well. Indeed in the book, the main savage character is named John, and in the movie (twice that I can recall), John is referred to as a "savage" by both Huxley (after propositioning her to have sex the "old fashioned way" - you know, 'Boning', 'The Wild Mambo', 'The Hunka Chunka'), and by Chief George Earle during the "Why don't you shove a leash up my ass" exchange.
Plus, there are the other references scattered throughout, such as the "behavioral engineering", being implanted into the prisoners as a rehabilitation, including the will and desire to carry out whatever task assigned (I'm a seamstress?!), as well as the similarities between Raymond Cocteau and Mustapha Mond. The book's title itself is actually spoken in the movie, by the antagonist "Simon Phoenix". In the scene inside the museum within the excavation exhibit, Phoenix is about to fire up the "ray gun" he got from the armory. Just before he fires the gun, he yells to Spartan "It's a brave new world! Too bad you've gotta go!"
Of course, the movie has a hollywood ending with John and Lenina living happily ever after, with the society forced into a position to make changes. The book, however, ends on a much more sour note, with John killing himself, and the society continuing unchanged.
But like I said, the movie isn't based on the book. More like "lightly inspired by."