The Singularity -- when our skill & knowledge & immense computing power transform us into... well... godlike beings. From a writer's perspective, it presents a problem. One can write stories leading up to the Singularity, about problems like rebellious AI. But how do you write a tale set after the singularity has happened? That's the topic of David Brin's short story, Stones of Significance.
Very thought provoking.