Recently, Carol Bartz’s executive assistant checked out to join Twitter.  The commute from San Francisco to Sunnyvale might have had something to do with that one. Now her top salesperson is jumping ship quitting, too.  Sales rep Joanna Bradford has left for Demand Media.  Valleywag reports Bartz learned about this by reading the news. Oops. No purple door prizes on the way out for Joanna.