Japanese, like all languages, is evolving. And, like most people who appreciate a language, I am not very happy about the changes. No doubt Urg and Og said the same thing back when somebody invented polysyllabic words. After all, I invested quite a bit of my life into learning Japanese and I hate to have it pulled out from under me now that I've finally gotten to the point when I can use it decently. (Yes, I know I invested more of my life into learning English, but that wasn't my decision now, was it?)
Japanese has changed significantly in both spoken and written forms. As a translator I need to understand both, but it is a lot easier to talk about the characters used in written Japanese in a blog. The general opinion seems to be that Japanese was only spoken to start with, with no native written language. This problem was solved by adopting Chinese hanzi, not surprisingly, because China was unquestionably the center of the East Asian world back then. ("Back then" being somewhere about 4th century, probably, when Buddhism and a lot of Chinese culture began showing up in Japan.)
Unfortunately, the ancient Japanese quickly discovered the same thing I found out in my first year of Japanese study: There are an awful lot of Chinese characters. This led (realize, I'm simplifying a bit here...) to the development of vastly simplified Chinese characters called katakana, used as phonetic characters, making it possible to write down native Japanese pronunciations fairly easily. The protected women of the upper classes in Heian Japan, feeling that the blocky Chinese characters and katakana were too masculine, preferred to use cursive Chinese, and so these flowing characters were eventually joined by a cursive phonetic character set, hiragana.
Eventually the Portuguese came along and taught the Japanese the alphabet, too, making for a quite complex set of glyphs.
Over the centuries, the language evolved... the number of kanji used has been steadily reduced (although they did have to add a bunch of characters used in names back in recently, because people whose names had been deleted felt justifiably upset by it).
After World War II, katakana became the script of choice for representing words from foreign languages, while hiragana and kanji were used to represent the Japanese language. In general, this still holds, although there are plenty of cases when authors or typographers use katakana to express strong emotion, for example, where an author using English might use italics or bolding.
Originally, imported words were expressed with appropriate kanji to represent the sound of the loan word, and in outstanding instances the meaning as well. This left us with brilliant coinage like 型禄, meaning catalog and pronounced kataroku. The two kanji mean something like "a record of types". I say this is brilliant because in addition to merely approximating the sound of the English, the kanji used also do a good job of expressing the meaning. This is very rarely seen any more, with just about everybody preferring to write it in katakana. Today, essentially all imported words are expressed in katakana, except in a deliberate example of wordplay once in a while.
But modern Japanese has gone too far now. One of my teachers at the summer intensive at Middlebury College said that a language doesn't have two words for the same exact thing... one of them fades away. That may be true, but in that case Japanese is still in the transitional phase where both appear. I don't know how many times I've had to translate something like, for example, "綺麗でビューティフルな云々," which literally means a "beautiful, beautiful" whatever. The Japanese author is using two different words for "beautiful," which is not in itself a bad thing, but with the exception of the source language they are identical! Needless to say, this tends to pose problems in translation... And as Japanese authors and advertising agencies go hog-wild with katakana as they import foreign words wholesale, we are ending up with a host of words in books and newspapers that most Japanese do not understand at all. When "governance" became a hot topic a few years ago, it came into Japanese in katakana, and the newscasters persisted in using it every day, even though they had to explain what it meant each time!
When new words are created in Japanese using kanji, for example 電話 (denwa; telephone), the two characters have a meaning. The first means electricity (actually, lightning...) and the second to speak or converse. Not a bad name for a telephone (from the Latin, meaning long-distance sound, I believe). When a foreign word is expressed in katakana, however, the significance of the roots are lost.
This leads to interesting situations such as the Japanese for the material glass (ガラス) being different from the drinking glass (グラス), or many Japanese thinking that マイコン (maikon; microcontroller) and マイホーム (maihōmu; my house) both come from the same English stem "my."
Modern Japanese is also experiencing the same sort of erosion of proper language by cellfones... In addition to cutting and chopping out characters until there's little left, young Japanese thumb-culture masters also cheerfully use what they think are English abbreviations (including a bunch that never were English to begin with), and emoticons of all flavors. :-)
Unless you stay up to date on your symbology, you haven't a chance of following this type of literature, and unfortunately it is beginning to spread from the cellfone and blog to the printed book.