Let me get something off my chest.
I’m sad that “Memoirs of a Geisha” is cast with women of Chinese descent in the three leading female roles.
I’m sad because this movie will reinforce inacurate stereotypes about geisha and Japan.
I’m sad because this says that there are no Japanese or Japanese-American women actors worthy of these leading roles. In fact, the press release from Sony/Dreamworks/Spyglass even says that casting began in Japan.

The primary cast was assembled after an exhaustive search, which began with several months in Japan and continued throughout Asia to find the perfect actor for each role.

I think it is safe to assume that the casting people started looking in Japan for obvious reasons, but that they could not find actors of the caliber necessary for the lead female roles who spoke English well enough.
Here’s something else that bothers me. Director Rob Marshall is using Liza Dalby, an American expert on geisha, to advise him on the movie.

“Memoirs of a Geisha” is also utilizing the talents of Liza Dalby, world-renowned geisha expert and author of many definitive works on the culture of the geisha, including “Geisha” and “Kimono,” as consultant in the making of this film.

Doesn’t that seem strange? Why not hire a Japanese expert on geisha? Language barrier again? Or would they never be able to hire a Japanese expert on geisha? (I.e. no Japanese from the Gion district of Kyoto would be caught dead advising for this film.)
The litmus test is how the movie will do in Japan.
“Lost in Translation” did pretty poorly in Japan, even though it was a cult hit outside of Japan. I think it’s safe to say that the audience for “LiT” was not the Japanese, and my Japanese friends who saw “LiT” in Japan were not moved by the film, again for obvious reasons. “Last Samurai” on the other hand, was well-received by the Japanese, did well at the Japanese box office. I feel that “Memories” is, like “LiT,” a movie by non-Japanese producers, with many non-Japanese lead actors, for a non-Japanese audience, but set in Japan.
That’s the difference, to me. If you can make a film about a culture that is not your own, and have it welcomed by those that you are portraying, then you’ve accomplished quite a lot. I have significant doubts about this production’s ability to do anything but reinforce romantic and innacurate stereotypes of Japan and geisha, and that is very depressing to me for many reasons.
The brilliant maneuver by casting these Hong Kong Kung Fu actors (Yeoh, Zhang) in these roles is that the studio can market this movie heavily to the Asian market beyond Japan (i.e. China, Taiwan, Singapore, Hong Kong, etc.)
Here are some other relevant quotes I’ve assembled:

[Memoirs of a Geisha] “received some criticism from the APA [Asian and Pacific American] community for perpetuating the stereotype of the overly exotic Asian woman and for being written from a white male’s perspective.”

- Casting all Geishas [asianweek.com]

[Arthur Golden's muse for "Memoirs of a Geisha," Mineko] Iwasaki agreed to an interview by the author because she thought she could help dispel “the Fujiyama-geisha image of a woman who sells herself to her customers.” She was shocked when Golden’s novel turned out to be a narrative that contradicted her very intentions.

- Ex-geisha takes objection to “Memoirs of a Geisha” [mainichi.co.jp]
I don’t plan on seeing this film and I have not read Golden’s book and I don’t plan to. I do plan to read Iwasaki-san’s book.

“There is much mystery and misunderstanding about what it means to be a geisha. I hope this story will help explain what it is really like and also serve as a record of this unique component of Japan’s cultural history,” writes Mineko Iwasaki. Geisha, a Life is the first of its kind, as it delicately unfolds the fabric of a geisha’s development. Told with great wisdom and sensitivity, it is a true story of beauty and heroism, and of a time and culture rarely revealed to the Western world.

- Geisha, a Life [by Mineko Iwasaki]
Finally, I’ll leave the last word for my friend Jim.

I’m sure it’s going to be a wonderful movie and all, but why is it that Hollywood always seems to use Chinese and Chinese-American actresses for Japanese female roles? (Michelle Yeoh is from Malaysia, Zhang Ziyi was born in Beijing and Gong Li was born in Shenyang, China.)
Do they really think it doesn’t matter?
Are there no Japanese actresses?

- Jim O’Connell: “Memoirs of a Geisha” Casting