Tweetake allows you to backup your followers, people you are following and Tweets with just one click.
Why bother to do this? Many reasons:

Twistory is a Twitter backlog mashup. Twistory provides an iCalendar feed (iCal, Google Calendar, ...) allowing you to easily browse...
Silentale creates a backup of your Twitter account along with your Emails and Social Networks accounts, so you can keep...