Twitter does not provide the option to export or import a list of users who are following your updates, so other services have cropped up to help fill this need. You can use an exported list of followers to track following count over time, make private notes about specific users, or even to manually reference when deciding whom to follow on an another Twitter account. If your Twitter account is ever compromised, a backup follower list can help you restore your account to its previous state.
Visit the Export.ly website (export.ly). Click the "Twitter" tab. Enter your Twitter username. Confirm that "Followers" is selected in the drop-down box. Click "Continue" to export your followers as an Excel file. This file includes each follower's Twitter handle, bio, location, follower/following count and more. As of March 2011, you can export up to 10,000 followers for free. Export.ly charges a one-time fee for exporting a larger number of followers.
Visit the TwitterExport service (twitterexport.com). Enter your username in the box and click "Export Followers." Select either Microsoft Excel or CSV as your output file. Click "Export." As of March 2011, you can export a maximum of 100 followers.
VIsit the MyTweeple website (mytweeple.com). Click "Sign in with Twitter." Grant access to your Twitter account when prompted; you may need to sign in to do this. Choose "Advanced Export" under the "Tools" menu. Click "My Tweeple's Premium Package" to upgrade to a paid account; you must have a paid account to export your followers as of March 2011. Complete the signup process and return to "Advanced Export" under "Tools." Check the "Followers" box. Select the fields you want to appear in your export, such as the name and location of each follower. Click "Export" to export your list.