All of them. Or, more precisely, anywhere you either: 1. may want to some day communicate officially with users, or, 2. wouldn't want someone else impersonat

All of them. Or, more precisely, anywhere you either: 1. may want to some day communicate officially with users, or, 2. wouldn't want someone else impersonating you Check out the list at http://www.usernamecheck.com/ http://www.usernamecheck.com/ (also handy for checking them) and then start registering. :) I wrote about social media cybersquatting in a blog post in October. Might be interesting to read about the experience the company I work for had: http://www.sitepoint.com/blogs/2008/10/31/do-you-own-your-social-media-identity/ http://www.sitepoint.com/blogs/2008/10/31/do-you-own-your-so... (Short story: someone else has their natural Twitter account -- @companyname -- and they were forced to use the somewhat clumsier @companynamedotcom instead)