Bryan Lowe, Chris Mayo, and a bunch of other advisors and contributors have launched an online Guide to Shōsōin Research, hosted by Vanderbilt University:

What are Shōsōin documents?

Shōsōin 正倉院 is the name of an eighth-century storehouse located on the grounds of the temple Tōdai-ji 東大寺. While it is most famous for its collection of treasures, including many objects that reached Japan via the silk road, it also preserves over 10,000 hand-written documents all dating from the Nara period (710–784). [...]

Why haven't I heard more about these sources?

English-language scholarship has barely scratched the surface of this rich source base. The primary reason for this neglect stems from the complexity of the collection, which has rendered it nearly impossible to use without specialized training. The manuscripts were cut apart and reassembled multiple times both in the eighth century and in the modern era. Publication further complicated matters, as the documents were again rearranged for the compilation of the Dai Nihon komonjo 大日本古文書 series.

There's also a blog and a glossary, both chiefly focused (at present) on how scholars deal with this cut-up mess of invaluable documentation: "The primary task of Shōsōin scholars in Japan is to figure out how these numerous fragments were once related to one another."

Lowe, Mayo, and the other contributs deserve a lot of credit for their work here. I didn't know diddly squat about Shōsōin documents before reading this page, but I do know how tough it can be to find the first foothold in a field like this — that one obscure reference book, tucked away only in a few major libraries, that lets you start exploring a topic in detail rather than in a popularized (or summarized-for-specialists-in-other-fields) form.

I suppose most people reading this also ready Language Log and are therefore aware that word aversion is the hip new topic these days. How timely then that a new cosmetics line recently launched in Japan is called "Moist, Diane."

Well, they also use other punctuatings, like "Moist-Diane" and "Moist Diane," but I don't suppose those are any better from the point of view of the moist-averse. Who, incidentally, should also appreciate the tag line: "For the moisture of all women. Moisturized skin. Moisturized hair. Moisturized body."

In conclusion, moist.

Here's another one from Nihon ongaku no nagare (previously on No-sword). This one is from Nihon ongaku no rizumu (日本音楽のリズム, "The rhythm of Japanese music"), by Koizumi Fumio 小泉文夫, and I offer it more as an example of applied Nihonjinron than a theory I take seriously.

Japan's year is divided into four seasons, like Europe's. In south and southeast Asia, some areas have only a rainy season and a dry season, while in others dramatic changes in humidity divide the year into six seasons, punctuated by monsoons. Compared to areas like that, Japan is rich in seasonal change without widely separated extremes in temperature, and this climate must surely be the most important foundation stone on which the Japanese way of life and artistic expression rest.

The work of farming is in preparing the soil, planting the seeds, nurturing the shoots, pulling the weeds, and finally harvesting the crop. The unity of this rhythm cannot be broken down. In music, too, there is the jo 序 or oki 置, then the richly evolving ha 破 or nakaba 中端, and finally the lively kyū 急 or kiri 切. This sense of unity has become the most natural form for expressing things.

The jargon in that paragraph refers to the famous concept of jo-ha-kyū and similar ideas in kabuki/nagauta music.

This would seem to be common to all peoples (minzoku), but such is not necessarily the case. For example, among hunting peoples and peoples built on the foundations of a hunting culture, short, repeated phrases and forms in which it is unclear when the work began or when it will end are common. Indeed, the work of hunting means leaping into action the moment that prey appears, but when prey will appear cannot be planned in advance. The day-to-day life is on a completely different rhythmic base from that of farmers, who know that a planted seed will certainly sprout but will not bear fruit until august, no matter how much of a rush the farmer may be in.

In the music of India and Europe, phrasal repetition is recognized, along with a large-scale structural sense, as a fundamental principle. In Japanese music, on the other hand, the principle of repetition is weak. To put it another way, within European and Indian culture, vegetable rhythms directed towards a beauty of structured form are blended with animal rhythms that reflect the moment-by-moment situation, but in Japanese music the vegetable rhythms seem to be prioritized.

Koizumi also seems quite convinced that traditional Iranian music has a very similar sensibility, but I don't know enough about that to comment.

From Kikkawa Eishi 吉川英史's "Katarimono" ni tsuite (＜語りもの＞について, "About 'katarimono'"), in Nihon ongaku no nagare (日本音楽の流れ, "The flow of Japanese music"), ed. Yamagawa Naoharu 山川直治), translation mine:

When "talking" (kataru), performers communicate events and circumstances in a way that the listener can understand. Their words, therefore, must be understood clearly. As a result, prolonging or freely raising and lowering the pitch of the sounds in the words tends to be avoided. If a performer does want to prolong a sound, they will prolong one that does not carry much meaning. For example, the last sound in a phrase, or particles or verb endings. [...]

The aim of "singing" (utau), on the other hand, is to express emotions, not events and circumstances. There need not necessarily be a listener, and it does not matter of the lyrics are not understood. As a result, words can be freely prolonged, advanced vocal techniques used to raise and lower their pitch, and rhythm of the words can be refashioned into a musical rhythm. This is why even though mikagura, saibara, and folk oiwake are sung in Japanese, they are completely incomprehensible, and sound like long vowel practice: "Aaaa, iiii, eeee."