The most valuable features are the collaboration and sharing.
The most valuable features are the Integrations, web site, and search.
With respect to our experiences with Confluence, we haven't had any issues.
What I like the most is the Wiki software that comes with Atlassian Confluence.
The look and feel and the user interface are great.
The solution is easy to install.
Integration within the solution is very good.
You can move workloads in between sub-servers so that you don't overload a portion of the server.
The feature I find most valuable is that Drupal is a framework and not only a CMS.
We use a part of the solution called Acquia. The personalization portion of this is the most valuable aspect fo the solution.
The most valuable feature is the Activity flow that is used to catch new activities.