Version 5.1 of GhostDoc is a maintenance release for the v5.0 users; includes minor enhancements and number of important bug fixes. Many of the fixes are relevant to the Visual Studio 2015 environment, so while everyone will benefit from this update, it is highly recommended for the Visual Studio 2015 users.
For the complete list of changes, please see http://support.submain.com/kb/a42/whats-new-in-ghostdoc-v5.aspx
For overview of the v5.0 features, visit http://submain.com/blog/ReleasedGhostDocV50.aspx