A mere 20,000 Twitter users steal almost half of the spotlight on Twitter, which now ropes in a billion tweets every week.

That means only 0.05% of the social network’s user base attracts attention, according to a new Yahoo Research study titled, “Who Says What to Whom on Twitter.”

Of the 260 million tweets with URLs that the study’s authors analyzed, nearly 50% of the tweets consumed were created by what they called “elite” users who fall into four categories: media, celebrities, organizations and bloggers. “Ordinary” users encompass everyone else.

Like findings in previous studies, the researchers for this one conclude Twitter resembles an information-sharing hub rather than a social network, with the top generators garnering huge follower tallies but not following their content consumers in return.

Unlike previous studies though, this one delves deeper into the production and flow of tweets. For example, while ordinary users consume a high number of tweets from celebrities and bloggers, those celebrities primarily listen to other famous people’s tweets and those bloggers listen to other bloggers on Twitter.

“By studying the flow of information among the five categories … our analysis sheds new light on some old questions of communications research,” the authors wrote in the 10-page study.

For access to a PDF of the full study, click here.

Do you think Twitter, which marked its fifth anniversary earlier this month, has evolved away from being a social network and transformed into just an information-sharing outlet? And if you think so, is that a good or bad thing?