I had this idea: A traditional Dyson sphere, what most of us singularity-as-a-setting writers now call matrioshka spheres (poor Dyson, to be remembered for the bad SFnal version), where lots and lots of little solar-powered polises live in huge cloud-like orbits around the sun. Gazillions of human analogues live in these things and 99.99% of them don't do much more than play World of Warcraft and their equivalents. Every once in a while one of these polises suddenly needs a lot more CPU power, maybe because its population is going after a boss-level, or there's a huge gathering thar requires a lot of environmental rendering. Whatever the case, the polises would like to have a mechanism for borrowing computrons from neighboring polises to do the rendering. Distance and orbital times make calculations difficult, but eventually promises of future returns on borrowed processing time become commodities traded just like the more predictable "hard" commodities of out-system manfacturing resources.
All of this is very boring, so specialized quasi-conscious AIs are tasked with figuring it all out. The post-human overseers who leave their entertainment realms to manage theses systems are rock stars, wealthy in some way, empowered perhaps to make decisions and dole out favors. The AIs, meanwhile, are looking through the optimization space to make surethe polis they're programmed to oversee has the best possible deals, maximizing speedups and minimizing slowdowns.
The day comes when someone is called upon to make good on a contract, and fails to deliver. Big. An adventure goes south, pixellated and trashed. And while the adventurers in the game are disappointed, the overseeing AI overreacts and pulls its contracts in, refusing to deal until its neighbors, some of whom are coming into a functional transactional range and others are moving out as orbits proceed, until they demonstrate significantly greater transparency.
Everything goes sour in the time it takes light to traverse the solar system twice as people realize that the promises the AIs have been making have no basis in real deliverables, and the promised adventures aren't going to happen and, worse, the promised entertainments to be delivered out-system to the manfacturing base that provides maintenance and parts for this bread-and-circuses civilization aren't going to happen, and the manfacturers either shut down or go slow-and-local. The intra-Mars orbit civilization starts to slow down as more and more resources are dedicated to preservation, and a great depression settles onto Sol.
And then the aliens invade, I suppose. Or something.