My So-Called BlogOnly five years ago, mounting an online journal or its close cousin, the blog, required at least a modicum of technical know-how. But today, using sites like LiveJournal or Blogger or Xanga, users can sign up for a free account, and with little computer knowledge design a site within minutes. According to figures released last October by Perseus Development Corporation, a company that designs software for online surveys, there are expected to be 10 million blogs by the end of 2004. In the news media, the blog explosion has been portrayed as a transformation of the industry, a thousand minipundits blooming. But the vast majority of bloggers are teens and young adults. Ninety percent of those with blogs are between 13 and 29 years old; a full 51 percent are between 13 and 19, according to Perseus. Many teen blogs are short-lived experiments. But for a significant number, they become a way of life, a daily record of a community's private thoughts -- a kind of invisible high school that floats above the daily life of teenagers.