title: Updating a value in a local app.config
body: <p>I've got an exe that reads some values from its local <code>app.config</code> file:</p>
  
  <pre><code>TargetDate = ConfigurationManager.AppSettings.Get("ThresholdDate");
  
  // and try to update with the current date
  ConfigurationManager.AppSettings.Set("ThresholdDate", "2011-09-01");
  </code></pre>
  
  <p>I thought it worked once, but am not seeing the <code>app.config</code> getting updated at all now.</p>