A tossup between posting here or in MPSIMS, but here goes: What former staples of SF have been made obsolete by advances in scientific knowledge? An obvious example would be all the stories depicting Mars or Venus as habitable.
Burroughs’ Pellucidar series. (That’s Edgar Rice, not William S.) No hole to the center of the earch at the North Pole.
Asimov retconned it in some of his later books, but in the original Foundation trilogy, all the interstellar starships (and large industrial fission plants) had vacuum tubes.
Heinlein’s Starman Jones (and others) have people making interstellar jumps using tables looked up in books and calculated (on the fly) using slide-rules.
Also, flying cars and jetpacks don’t seem very likely anymore, dammit.
Fenris
“It’s the 21st Century. I was promised flying cars. Where are the flying cars?” 
There was a famous SF cover showing a space pirate with a slide rule in his mouth. And a lot of the old space opera (like Doc Smith) featured slide rules.
How about his Barsoom series? The airships on the covers look exactly like boats. Plus radium doesn’t explode. And there is air and water on Mars.
True. I just thought Lumpy covered the Mars/Venus issues in his OP. So I didn’t raise the specter of John Carter, or Carson of Venus.
True, I just love the flying boats on the covers. Love laughing at them.
Hey Hey Hey!!! I see nothing wrong with those books!! 
Ahh, slide rules. I would love a refresher course. I’d forgotten about them – they were a rite of passage…
OK, I’ll buy the unlikelihood of slide rules and books – but, no flying cars in my future? no jetpacks in my future? You’re breaking my heart, Fenris. The Death Calculator gives me life until 2033, I think… surely we’ll have them before then?
Poul Andersens’ protagonist Dominic Flandry smoked.
Star Trek had the Eugenics War in 1990 something.
1984, anybody?
Many old science fiction writers (and filmmakers) depict the computers of “the future” as being incredibly sophisticated, but with little or nothing in the way of a visual display system. That always cracks me up, not just because it’s so wrong but because it seems as though this should have been something people could have easily predicted. “Maybe in the future you’ll be able to hook a computer up to like, a television kinda thing, and then it could show you stuff!”
Within its own timeline…
“2001: A Space Oddysey” by Arthur C, Clarke
no hotels in space, or regular commercial flights to space
no permanent bases on the moon
no manned flights to Jupiter / Saturn (movie/book)
no “rail gun” rocket launching (book)
Isaac Asimov wrote a short story about how no one was able to reach the summit of Mt. Everest on account of the Martian base up there…Which wound up being published after Mt. Everest was climbed.
Also, all “first trip to the moon” stories, from Jules Verne to Robert Heinlein.
Any story that portrayed Mercury as having one side always facing the sun. Asimov had a couple of these. One was a Powell/Donovan/robot story called “Runaround”. He also wrote a novel called “Lucky Starr and the Big Sun of Mercury”. I seem to recall another short story about a murder that takes place on Mercury but its name escapes me. When these stories were reprinted he would always give a little introduction remarking that they were obsolete.
I seem to recall reading some articles (perhaps one or two by Asimov himself) that have listed scientific developments that have obsoleted some sf stories.
HHGTTG: DNA tests clearly reveal we are descended from the peaceful ape-like creatures and not from telephone sanitizers and hair stylists.
I also don’t think the Volgons destroyed the planet or that Slartibartfast designed the Fjords. But perhaps this discussion belongs in Great Debates.
In Neuromancer serious quantities of RAM were measured in `megs.’
I think you’re thinking of “The Dying Night” - it took place on Earth, but the Mercurian rotation played a key role in it. Also, as the author of the link points out, the plot turned on the idea of a compact microfiching “pen” that scientists would use to copy data, papers, etc. That little device will never go to production, because of downloading.
Space:1999
I thought Maya the shapeshifter was a babe, but my real infatuation was for the nuclear-powered Eagle class ships. They could regularly go from the Moon to a planet’s surface & back without re-fueling.