Just once, I'd like to see a story in which there's a planet-wide network of interlinked computational elements and/or life forms, and yet it turns out that the thing isn't sentient.
There's a trope, or maybe I mean a plot, so common in sf as to be practically a subgenre: humans land on a heretofore-unexplored planet; they encounter plant life that's disturbingly similar across the whole face of the planet, or a mysterious crystalline lattice structure that extends through the entire planet's structure; they think "Good thing there's no sentient life here" or "Too bad there's no sentient life here"; in the end it turns out, to everyone's (except the reader's) vast surprise, that the planetary interlinked whatsis is in fact sentient.
I'm pretty sure I've read stories from the '30s or '40s with more or less that premise and plot, so I'm pretty sure that it was already familiar to me and unsurprising by the time I read the relevant 1971 Ursula Le Guin story (link is to Fictionwise version in case you want to buy it—it was a Hugo nominee, after all, though it's not among my favorites of her stories).
At any rate, even if the idea was new in 1971, it's not new now. And yet at least three stories featuring basically this plot have appeared in the last three of Gardner's Year's Best SF series, written by major well-known authors. (To be fair, I haven't yet finished the relevant story in the latest YBSF, so it might surprise me yet. But the author's been laying on the hints pretty thick so far.)
So the idea clearly continues to have tremendous appeal to sf readers and writers and editors. But it has very little remaining appeal for me. More specifically, I don't mind the idea of planet-sized intelligences at all; what bugs me is that this idea continues to be used as (more or less) a surprise twist ending. It's gotten to the point that as soon as characters in a science fiction story encounter some mysterious phenomenon that everyone thinks is the nonsentient product of natural forces, I assume that it's going to turn out to be sentient, and I usually turn out to be right in that assumption. (Which I suppose is gratifying, given how often my other assumptions about life turn out to be wrong.)
Isn't it possible that there are mysterious natural phenomena out there that don't indicate sentience? I suppose we can never be certain that a given phenomenon isn't sentient—for all I know, the atmosphere of Earth is sentient, but in a way that's so incomprehensible to us that we'll never know it—so I suppose another factor in the kind of story I'm complaining about is that the humans nigh-inevitably figure out that the aliens are sentient and make contact with them (or vice versa) at or near the end of the story.
So anyway, I'd love to see a story where the whatsit turns out not to be sentient, but I'd also be happy with one where the discovery of sentience isn't the point of the story.
More generally, I have this recommendation for authors who've come up with a cool idea that they want to use as a surprise twist ending for an sf story: think about what kind of story you could write if you instead made the surprise discovery the middle of the story (or even the beginning of the story!), and continued on after that. In many cases, the resulting story will have a lot more emotional depth and will result in much more interesting character arcs; the point of the story becomes not the surprise at the end, but the effect that a change has on a character (or on a civilization or an alien life-form). Think about how you could use your story to say something interesting about people or about a person, rather than as a way to try to fool the reader.
You may end up deciding to go back to the surprise twist ending; clearly there's still plenty of life in the notion of surprise twist endings, even if they're rarely to my own personal taste. But I think it's a useful exercise anyway, and it may, in a small way, change how you think about stories.
One caveat: if you do take this approach, you generally shouldn't build up the twist as if it's going to be a surprise twist ending. If the editor or the reader becomes too convinced that this is yet another story with the same surprise twist ending they've seen a hundred times before, they may stop reading before they find out that's not where you're going at all.