It's used as a CMS platform for our public marketing and e-commerce websites. It is used by our consumer interactive group as well as e-commerce group. The number one problem it addresses was speed to make changes and roll out new content. Our previous systems were not efficient at allowing business users to author and publish content in a timely manner.
Episerver is a great platform for any team with .NET MVC experience. It is one of the few enterprise CMS/E-Commerce platforms that is truly .NET MVC. This allows your development team to take full advantage of all the latest .NET capabilities. It does a good job of being able to handle multi-tenancy, and many of the authoring tools are simple and make sense.
I can't think of any scenarios where it could not be successfully deployed.