TwitterExport.com was developed by Angel S. Moreno of PHPMine.com for the purpose of showcasing a command line script which goes by the name of "PHP Twitter Export". He created the script in his spare time in order to use it for archiving purposes. He later realized the tool had potential for a being a powerful marketing tool. He quickly developed a site around the script in order to share it with other with the hopes of improving the tool with the opinion of others.
The web-based version of PHP Twitter Export 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.