I'm running an OA campaign right now (non-Rokugan, but with a few Rokugani concepts, like the clans), and it's working out great. My players leapt at the chance to play races other than the traditional elves/dwarves/little people, and the only real problem has been a bit of bickering over who got to be the group's samurai (I only allow one, as I think there are enough classes available that everyone should be able to find something different that interests them).
The biggest strain so far has been making the adventures feel "asian" enough. It's kind of difficult for a westerner who doesn't have a whole lot of knowledge of asian culture to get in the proper mindset. One thing I've done is play up the concept of "honor" rather than good vs. evil, and emphasize that lawful characters will be more respected/trusted than neutral or chaotic characters.
As for why I chose not to use Rokugan itself, I honestly found the setting a bit too restrictive. By my estimates, Rokugan only uses approximately half of the total content in OA, and it's all just too good to ignore any of it. What I've done for my homebrew setting is to steal liberally from any and all asian style forms of entertainment I'm familiar with.

Specifically, the setting has been influenced by the Final Fantasy games, anime, manga, and movies such as
Crouching Tiger, Hidden Dragon.
On a related note, if anyone knows where I could find some variant combat rules to allow for CT,HD style stunts, a link would be much appreciated.
