Different from most other countries, Japanese college students virtually have only one chance to get a permanent job. Namely, they want to or need to find a job and start working from April of the year of graduation. (N.B., the Japanese school year starts from April and ends in March.) On December 1st, junior students officially start attending explanatory sessions, interviews and other activities to find jobs. Many expect to find a job by the start of their senior year. On October 1st of the senior year, students who found jobs are officially offered a job, which is the official end of their job finding activities. (Those who could not get an official offer may have to continue searching for a job afterwards.)
One important characteristic is that a Japanese company does not generally require the new graduates to be an immediate asset for the firm. Therefore, students do no need to have some experience in relation to the job (such as intern or part-time job) during college. What the companies do is conduct systematized training and educate them.
The education, of course, needs a lot of time, money and effort. It would be a loss of an "asset" if those educated employees easily switch jobs. So, another important trait is that compared to many other markets around the world, the Japanese job market is relatively illiquid and Japanese companies traditionally offer lifetime employment.
The other important issue is that this is virtually the only chance a student may have to get a permanent job. Of course, there are some successful stories where a worker changed her status from a part-time to a full-time position, but at this time, they are exceptional. So, Japanese juniors are zealous and desperate to find a good full-time job during this period of simultaneous recruiting.
As a result, juniors tend to quickly follow the trend of the society. In a recent research by Dentsu Public Relations, about half of juniors are using social networking sites to find jobs.
Different from the US, LinkedIn is not very popular in Japan. Therefore, the site most used for finding jobs is Facebook. According to the research, some students use Facebook as a digital business card and some use Twitter as a tool to collect informal information.
I am not sure whether the Japanese system of simultaneous recruiting of new graduates is good or not, but at least, in this world where SNSs are widely used, it is good to learn to use it as a business tool at a relatively early stage.