"Capture" Your Readers

This caught my eye on the ADD THIS web site. I can understand that user authentication will cut down on spam, but the capture of information bothers me. The script will capture your Twitter, Facebook or Google+ username as well as any public information.

From the website:

If you missed the announcement last week, we’ve added Social Sign In (SSI) to our plug-in suite. Integration to your site will allow users to log in using their existing social accounts on the three largest social networks - Google, Facebook and Twitter. Your users will have a more personal connection to your site while providing you with accurate authentication and demographic data.

If you use this script, I would appreciate if you stop back by and let us know how it works. I know that privacy is just a concept in today's world, but it still matters to some.