title: What is the difference between the "Guest" and the "Not logged in" customer groups in Magento?
body: <p>What is the difference between the following customer groups in Magento:</p>
  
  <pre><code>Guest
  </code></pre>
  
  <p>v</p>
  
  <pre><code>Not Logged In
  </code></pre>
  
  <p>To me these are both the same but when are each used?  I believe this to be a source of a bug I am investigating as they both use different customer group id's 0 and 1 respectively.</p>