The woman that poses as Barack Obama on all his social networking websites such as Facebook, MySpace, and Twitter is connected to the far-left organization MoveOn.org.
For those scratching their heads, the President in theory is a member of these websites. However, he obviously isn't responsible for typing in the little messages that are going out to his followers almost 24 hours a day, seven days a week.
On Friday, the Wall Street Journal revealed the identity of the current Twitterer as Mia Cambronero.
Our friends at Sweetness & Light have discovered that she is a senior fellow at the New Organizing Institute which is described by Discover The Networks (h/t Story Balloon):

On
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For the fourth straight weekday as Barack Obama vacations, he received better coverage on the broadcast network evening shows than the non-vacationing John McCain. Without fresh video of Obama, the CBS Evening News came up with a new way to tout Obama's campaign as they compared the Web sites of the two candidates and declared Obama's far superior. Reporter Daniel Sieberg asserted “McCain's Web site is still playing catch up to Obama's use of cyberspace.” Turning to “Web design expert Doug Jaeger,” Sieberg echoed Joe Biden in applying the term “clean” to Obama as he highlighted how “Jaeger describes Obama's site as clean; and McCain's as cluttered.” Jaeger complained about
Updates below. (Close look at whiteboard in video calls Ann Coulter a "whore," etc.)
Barack Obama's campaign has gotten itself into a bit of trouble over a Myspace profile.