Metatropolis by John Scalzi (editor& author), Karl Schroeder, Elizabeth Bear, Jay Lake, and Tobias S. Buckell
Most compilations of short stories are hit and miss because while there is an overarching theme, the individual stories are of variable quality. Metatropolis tackles this problem by having all the writers writing in the same world (and of course having good writers and the amazing John Scalzi on the team I'm sure helped). They swapped ideas over how to build this world while they were each writing. The result is really good.
The near-future post-apocalyptic feeling is built into every detail in these stories, and the ideas that are created are amazing. I really wish this collection could be expanded into a full series to further explore the world these authors built.
I love that MMO's have been taken to a new level, and things like Amazon's mechanical turk are twisted slightly to show what could happen.
As with most post-apocalyptic novels, the tone of the stories are somewhat gritty and have a sense of removal of emotion in the wake of disaster. I loved it.