There is sex in the novel, and one scene in particular is graphic in its detail. The sex is described in an overt tone that is dirty and casual, pornographic and scientific. But this layer of grime is generally used to cover the human emotions at work. Case may think his relationship with Linda Lee is a carnal one, but her death still greatly affects him.
Likewise, Case and Molly start their relationship with casual sex, but by the novel's end, their relationship has grown significantly more complex. Molly's past as a "meat puppet" prostitute (11.142) provides a significant clue as to the type of person Molly was, is, and will become as the novel progresses, and that has a profound affect on Case.
Shmoop is giving this novel an NC-17 rating for the gratuitous detail of the sex in Neuromancer. But the intent and purpose the sex in relation to the character development is never as gratuitous as it might initially seem.