This unofficial tool provides a migration from an RSS Reader (ie. Google Reader) to following people on Twitter. The process is not automatic, but instead finds feeds for each of your previously subscribed RSS Feeds, and allows you to choose Twitter feeds and follow them in one simple step.
UPDATE (2011/11/02): Feed folders are now supported.



Disclaimer: While this does not make any changes to your Twitter account on its own, clicking the ‘Follow’ buttons will actually follow users for you. I primarily built this tool for myself, so please use it at your own risk. It is free to use, but comes with no warranty and I am not responsible for its use or effects. There is no “undo button” anywhere on the site, the changes are permanent and go to your Twitter account instantly.
Make sure that you have logged-into Twitter before starting. Otherwise, the ‘Follow’ buttons will not display the correct state.