"Library of Congress plans to archive Twitter posts Privacy concerns raised, but tweets offer slice of history By Jon Swartz USA TODAY SAN FRANCISCO — If you tweet this, it will be in the Library of Congress. On Wednesday, the library said it has acquired Twitter’s service started four years ago. The implications for Twitter’s more than 100 million users could be huge: it runs 55 million tweets every day, which means billions of tweeta are being archived." The entire article is in today's (April 15, 2010) USA Today newspaper.
In the same article, "Google is introducing Google Replay, a feature to search historical public tweets around a specific topic and date."