All over the place.
Mine campaign is generally Western flavoured with a few twists.
Enforcement of Culture by crunchy bits:
I enforce cultural changes, through feats like Forgotten Realms does, in fact I steal liberally from their feat least.
I also have regional variants of rangers: horse nomads, bow masters, and defensive hoplites. I accomplis this by swapping out the virtual feats of ambidexterity & two-weapon fighting for one of these three sets: mounted combat & mounted archery, point blank shot and precise shot; and finally dodge and expertise.
My kobolds, one of the most important races in the Southern lands (Think Arabic) have a variant druid who deals with vermin instead of animals.
Monks, which I also call Mythic Heroes, are like rangers in that they have variants. Northern monks are master wrestlers, Isle Elf (think Classical Greek) monks favor holds and joint locks, Orkaan monks favor throws, et cetera. I do this by swapping out the stunning attacks, deflect arrows, and improved trip abilites for different feats detailed in Oriental Adventures.
Religion plays a critical part in my campaign world too. Every region has a very different religion, and I let that shape the politics and the moores of the region. This means strict control of domains and clerical prestige classes. I also have a couple of regions of anti-theists. In these regions I dumped a lot more healing spells into the bard spell lists and let them become the spiritual center for these lands. My Arabic-esque lands rotate around the wisdom of the sufi poets, and my Greek-esque elves follow the wisdom of the philosopher-kings.
Noncruncy enforcement of flavour:
Naming conventions. I use real-world languages to name the various characters and places in the game. Each region gets a language or a set of languages, depending on the vastness of said region. People from my Heartlands are given French, German, Italian, Dutch, English, or German names. My Kobolds all have Farsi names. My Dwarves are given Finnish names. And my Orks get to pick from Russion or Mongolian names.
I've found that doing so helps give and immidiate flavour to a region, and lets me crib on some cultural tidbits when I have to.