This is a topic I'm glad to see threadcromancied, because it's something I've had to give some thought to lately. My home campaign has made it's way to our oriental section, and I'd spent a fair bit of time doing some reading (both real books on oriental culture & mythology, and also RPG books) to try and get it just right.
The big concern for me was that historical accuracy maybe wasn't the way to go if I wanted the players to treat the land as true travellers from medieval-ish Europe would. Even thirty years ago, the east was a slightly more exotic place, hence the rather quaint preface to the first Oriental Adventures book: nowadays, the oddities of Japan and China's history and culture are much better known, especially in geek circles. In a way, throwing in historically accurate Samurai was "too safe".
In the end, I threw together some bits from Kara-Tur and Rokugan for the shell of the world, and then made a big shift in the way divine casters were portrayed - I took Clerics and Paladins out completely from the two Lung empires and gave them the Magic of Incarnum classes instead. This helped portray their religion as truly foreign, and also gave a hook to keep the cultures different - without easy access to Remove Disease or Raise Dead, Kara-Tur suddenly seemed a lot more than just a re-skin of D&D normality. (OK, so there may be some Spirit Shamans in the Tibet-esque region, but the principle stands.
)
I also have a Great Wall of China-esque thing which is actually a huge Incarnum channeling device, essentially built by an ancient empire to help keep the soul energy of the empire recycling. All this meant that I got to use Incarnum in a slightly better way than just saying "Er, there's an alternate magic system that's always been there, honest" and toss a few country details and plot hooks in as well. I used some typical OA classes and races as well as adding in some others: Catfolk seemed a good fit, as did the Dvati (a very strange race from the Dragon Compendium).
As other posters have said, you don't treat your medieval or Tolkein-esque settings to huge complaints about the "lack of proper Spanish material" or "incorrect definitions of 'priest'". D&D has always been a game that held other cultures at gunpoint, took their precious things, threw them in a big pot and then swam in it naked while giggling maniacally to itself and wondering how much XP their deities would be worth. An oriental game setting is, ultimately, still a game setting and should be treated accordingly - historical accuracy being way below the concerns of general purpose fun. ;-)
The big concern for me was that historical accuracy maybe wasn't the way to go if I wanted the players to treat the land as true travellers from medieval-ish Europe would. Even thirty years ago, the east was a slightly more exotic place, hence the rather quaint preface to the first Oriental Adventures book: nowadays, the oddities of Japan and China's history and culture are much better known, especially in geek circles. In a way, throwing in historically accurate Samurai was "too safe".
In the end, I threw together some bits from Kara-Tur and Rokugan for the shell of the world, and then made a big shift in the way divine casters were portrayed - I took Clerics and Paladins out completely from the two Lung empires and gave them the Magic of Incarnum classes instead. This helped portray their religion as truly foreign, and also gave a hook to keep the cultures different - without easy access to Remove Disease or Raise Dead, Kara-Tur suddenly seemed a lot more than just a re-skin of D&D normality. (OK, so there may be some Spirit Shamans in the Tibet-esque region, but the principle stands.

I also have a Great Wall of China-esque thing which is actually a huge Incarnum channeling device, essentially built by an ancient empire to help keep the soul energy of the empire recycling. All this meant that I got to use Incarnum in a slightly better way than just saying "Er, there's an alternate magic system that's always been there, honest" and toss a few country details and plot hooks in as well. I used some typical OA classes and races as well as adding in some others: Catfolk seemed a good fit, as did the Dvati (a very strange race from the Dragon Compendium).
As other posters have said, you don't treat your medieval or Tolkein-esque settings to huge complaints about the "lack of proper Spanish material" or "incorrect definitions of 'priest'". D&D has always been a game that held other cultures at gunpoint, took their precious things, threw them in a big pot and then swam in it naked while giggling maniacally to itself and wondering how much XP their deities would be worth. An oriental game setting is, ultimately, still a game setting and should be treated accordingly - historical accuracy being way below the concerns of general purpose fun. ;-)