title: When NOT to use Cassandra?
body: <p>There has been a lot of talk related to <a href="http://cassandra.apache.org/">Cassandra</a> lately.</p>
  
  <p>Twitter, Digg, Facebook, etc all use it.</p>
  
  <p>When does it make sense to:</p>
  
  <ul>
  <li>use Cassandra,</li>
  <li>not use Cassandra, and</li>
  <li>use a RDMS instead of Cassandra.</li>
  </ul>