Hi David,
We have had a single customer work with a partner to implement such an integration. Essentially, in that scenario (as currently implemented), users are able to go to a project in Workfront, click on a custom page related to the project and click a button that automatically creates a new "notebook" in Evernote (a single notebook can contain lots of different notes). It also adds existing project team members with permissions to that notebook in Evernote.
Once created and linked. Users can later click on this custom page for the project and view all notes associated with the notebook / project. They can simply click on the note and it will bring up Evernote to display the details. In many ways, this is essentially just another way to capture qualitative information on a project while allowing users to continue to use tools that they are already leveraging in the field and through mobile apps, etc.
The downsides of the existing approach are, of course, that while that information is easily viewable in Workfront, it is not actually included in the update streams, etc.
I imagine there are other use cases and approaches. Thanks for the question.