I've encountered an error (and so has another Drupal developer) when updating to the current version of Acquia's Dev Desktop Control Panel (1.2.40) for Mac OSX.

Upgrading from a previous version to the current version can destroy the Apache configuration settings needed to direct your web browser to the appropriate directory on your local computer. As a result, any existing Drupal installations that you created on your laptop will break. Instead of going to the intended website, you will be directed to the empty Drupal site that Dev Desktop creates upon installation.

The bug will not destroy your MySQL databases or your Drupal code, just the configuration needed to make it display in your laptop. However, repairing the configuration can be time-consuming, especially if you have multiple Drupal sites set up on your local computer. I recommend making a backup of the app or at least its configuration files (vhosts.conf and dynamic.ini) before attempting an upgrade.

You can find a more detailed description of the bug and instructions for how to fix things if your sites get hosed on the Acquia forum: https://network.acquia.com/node/1887722