TwitterExport.com is in Beta. This means that only the first 100 followers or friends will be exported. Currently, only 150 requests can be made to the Twitter server per authenticated twitter user. As you use TwitterExport.com, requests are made tot he Twitter server as the twitter user Tweexport. The limitation of 100 followers or friends is so that as many people can use the tool without having to provide a user name and password. The tool is currently being modified so that each export is counted towards an authenticated user.
Stay Tuned at http://www.twitter.com/tweexport.