I’ll admit it—much though I love stories in which the culture is one of the most prevalent characters of all, I can’t really think of one stunning example of having done the grand culture-build and made it stick. Instead, most of what I’ve got is a lot of practice cases, going partway into the idea but never quite fully engaging.
My primary game’s managed the most, if nothing else because I’ve had so long to add on to the cultures. I don’t really stray that far from canon, at least not with my Celestial Bureaucracy—granted, I’ve added things that have seeped into the player perspective, including Olathe’s memetic Force of Nature status, but for the most part it’s all the usual goals/restrictions/Things One Does Not Do. With my main group, this works out pretty well—two of the PCs work around and with it, one of them is himself a product of the culture, and the ones who are no longer in the group have had varying reactions, connections and clashes with it. What’s been interesting, though, is the solo game; I didn’t quite manage buy-in with the sole PC (in-character this is odd, given she’s been backstory-immersed for as long as she’s been sapient), but on the other hand, one of the largest obstacles to her primary goal is the fact that one of her closest friends does buy into said culture, very much so, and is convinced with good reason that she has broken several of its most important tenets. Awkward.
One of my biggest incidental culture-builds was as a player, when I was playing Tuyet. She was my first real attempt at “constrained by the culture, but uses it as a weapon”–along with deliberate character development—so I spent a good portion of the first arc either finding things that seemed like reasonable ways that she could use her culture as a weapon, or building both culture and subculture around her to explain her actions (including the Fifty Laws of Spycraft, of which I can sadly only remember Rule 47, “Use everything that comes to hand”).
I’m going to put it all to use in my next game, though—I’m going for a multiversal RPG of manners, with a nice hefty side of intrigue, a dash of conspiracy and a little bit of “what happens when mutually exclusive magic systems end up extending to the same areas” for dessert. If I can get myself to start the setup, this will be fun.