Three Useful Tools:
MyPermissions, SocialMention, HackerFollow
MyPermissions (was http://mypermissions.org/) Checks for third party application access to your Facebook, Twitter, Google, Yahoo, LinkedIn, Dropbox, Instagram, and Flickr accounts.
SocialMention (was http://www.socialmention.com/) Allows you to do keyword and phrase search across more than one hundred social media sites including Twitter, Facebook, FriendFeed, YouTube, Digg, Google, etc…
HackerFollow (was http://hackerfollow.com/) follow comments and posts by your favorite Hacker News contributors
See also HNReplies.com Created by Dan Grossman