BackupMyTweets joins a couple of the other backup services we highlighted built around the fact that Twitter doesn’t store your tweets forever. First things, it is free and does not require your Twitter password.
You have the choice to tweet whether you used the service or not. I chose not. You then authenticate at Twitter via OAuth and it will send you a direct message with a link to get the backup.
I was able to download in HTML, JSON or xml making it easy to manipulate the data or just save it for later. Go get your stuff before it vanishes into the ether.