I was researching online this past month and found out that if you are a member of twitter and posted some tweets, they are going to be archived in the Library of Congress. Just think...the daily activities that everyone writes about will be in the Library of Congress. The News posted at the Library of Congress states: "The archive follows in the Library's long tradition of gathering individuals' firsthand accounts of history, such as "man on the street" interviews after Pearl Harbor; the September 11, 2001, Documentary Project; the Veterans History Project (VHP); and StoryCorps. While the Twitter archive will not be posted online, the Library envisions posting selected content around topics or themes, similar to existing VHP presentations."
If you would like to learn more about this, you can visit Library of Congress or the The Twitter Blog.