Twitter is totally "in" in Japan. Everybody who matters are doing it, except for a few "old media types" who still have not figured out how to stick that blue-and-black "t" button on their web-version newspaper articles.
Japanese twitter-stars, such as @chikawatanabe and @hisamioh, have mentioned that the Japanese language has lots of advantage in this short-form style. Just one Kanji, the Chinese character, signifies a concept, so you can easily express a concept with just a few letters. As a result, Various characters used in Japanese, including two forms of phonetic characters (hiragana and katakana), kanji and alphabets, the mere 140 character can turn into a rich, funny or serious piece of art, freely transform from a petty personal mumble to a intellectual political or philosophical discussion.
Haiku is globally known as the shortest form poem in the world, and I often compare Twitter with less known older cousins, "renga", or "continuous poem". In an ancient noble world, people gather in a room and one person starts a short haiku-like short poem, the next person adds another few lines, then the next person continues on adding to the second person, and the play keeps on going.
In Japanese twitter-sphere, this type of continuous conversation often happens, with sometimes 4-5 people mentioned like a chain and each person adding his/her say. It is made possible by the kanji's rich expression power that saves number of characters, as @tokuriki, one of the top Twitter-stars, points out. If I try to do the same in English, I quickly run out the 140 characters limit.
What is important here is the communication itself, more than the contents. People tweets to have conversation for conversation purposes, not because the content is important. Of course, for some people - like me, sometimes, to broadcast my contents such as my blog entry is the main purpose. But more often I do it for conversation purposes.
You have to have some contents to communicate. As a telecom industry person, I often think of the contents as the highest layer thing on top of the communication tools such as mails and phones, but I think these days I should think it as a reverse, in many cases - contents as a vehicle of communication.
Twitter is rather a "naked" form of communication, with each participants giving out his/her idea with it, although the 140-character limit is giving some sense of structure. But in "renga", for example, the poem - the art of words - were more the vehicle of communication for participants than the art itself as a purpose. You can think of many games and other excuses for gatherings - card games, hobby groups, book clubs, backyard barbecue and so on. In a broader sense, many "high-brow" art, such as fine art, theater and literature, can be considered the "vehicle of conversation" for the people in the high society. The providers of the art certainly do it for the sake of art itself, but for consumers, the art piece is the mixture of the value itself and the tool for the communications with the people in the same class.
In that context, Facebook is an interesting mix of the "naked" communication form and various "vehicles" such as network games and silly social apps. My son's timeline is full of meaningless "surveys" or "riddles", and that is what the communication is. The youngsters are more enjoying the communication, less the contents. The right mix is the key for success here.
The telecom industry has been providing the tools for "naked" communication for more than 100 years. We in the industry often think the contents is king and is more important than telecom. But I suggest to reverse it, from time to time, and consider "contents" as the vehicle of communication and people value the communication the most. Person-to-person communication, over the human history, is the king.