(noloc)

Starting 10/10/2010, Twitter will begin transferring all of your tweets to the Library of Congress for archiving. Tweets that are 24 weeks old (6 months) or older will be saved forever, and you will no longer be able to delete them. By using #NoLOC.org, you continue to use Twitter like normal, but when you tweet turns 23 weeks old, we'll delete it automatically.

Just sign in with Twitter to use NoLOC.org, and all of your tweets that
include the hashtag #noloc will not be sent to the Library of Congress
for archiving. It's that simple...
(more)