[Case had] watched [Linda's] personality fragment, calving like an iceberg, splinters drifting away, and finally he'd seen the raw need, the hungry armature of addiction. He'd watched her track the next hit with a concentration that reminded him of the mantises they sold in stalls along Shiga. (1.44)
Notice the description given to the mentality of the person constantly using drugs. What other character, or characters, could we describe as having a personality "calving like an iceberg"? What does this say about drug use? Hey, wait, why are they selling mantises?
Get just wasted enough, find yourself in some desperate but strangely arbitrary kind of trouble, and it was possible to see Ninsei as a field of data, the way the matrix had once reminded him of proteins linking to distinguish cell specialties. (1.127)
Case uses drugs to feel connected like he did in cyberspace. The feeling of being high replaces his computer addiction. We all love Twitter, Case, but, jeez, keep it reasonable, man.
The pill lit his circuits and he rode the rush down Shiga to Ninsei, then over to Baiitsu. (1.144)
Another connection between drug use and technology. This time, the drugs make Case feel like a machine, perhaps suggesting that they suppress his human side.
"Demerol, they used to call that," said the Finn. "[Riviera]'s a speedball artist. Funny class of people you're mixing with, Case." (7.56)
Although Case and Riviera are two totally different characters, their recreational drug use and their dependence on technology connects them, despite their best efforts.
Aerol, with no particular provocation, related the tale of the baby who had burst from his forehead and scampered into a forest of hydroponic ganja. (8.60)
Drugs can make you experience things that aren't really happening, but if you experience them in your mind, then how will you know the difference? Hint: ask the sober people.
The bright eyes met [Case's]. "Of course it does. That's part of it, isn't it?" (8.73-74)
Pain and pleasure, pleasure and pain. The two go hand in hand in the drug game.
[Case's] brain was deep-fried. No, he decided, it had been thrown into hot fat and left there, and the fat had cooled, a thick dull grease congealing on the wrinkled lobes, shot through with greenish-purple flashes of pain. (11.8)
Lovely. This is easily the best description for a hangover ever put on paper. Notice how when Case uses drugs the descriptions are all bright lights and wonderment. And now, well, not so much. See the difference a day makes?
The drug hit him like an express train, a white-hot column of light mounting his spine from the region of his prostate, illuminating the sutures of his skull with x-rays of short-circuited sexual energy. (12.38)
The writing style connects the promise of being machine-like with the use of drugs. Trains, white light, sutures, x-rays. It all sounds cool enough, but it's masking some pretty horrific physical consequences.
The clarity of [Molly's] sensorium cut the bite of the betaphenethylamine, but Case could still feel it. He preferred the pain in her leg. (16.28)
Case finds a substitute for the drug in his connection with Molly and her pain. It shows how far Case's character has developed since Chiba City where his connection to the drugs blocked his ability to connect with Linda Lee.
[Case] spent the bulk of his Swiss account on a new pancreas and liver. (24.44)
Ah, the ambiguous ending. It's never fully explained why Case gets a new pancreas and liver. Did he want to take up drug use again or did he just want to be free of the limitations Armitage put on him?