We had a pretty basic problem to solve. We had a set of nodes within an Drupal organic group (OG) and on all of these pages I wanted to display a field from the base entity for that group. So in the Views module, we just wanted to create a simple block to display this field.
So this seemed like a case where you would setup a view with a contextual filter for the current node, then add a relationship that ties in the OG some how. Unfortunately this proved to be quite troublesome. The language surrounding some of the filters/relationships left a bit to be desired. But luckily, it was much easier than this.
The very basic recipe for getting information from the OG base entity:
Contextual filter: Content: Nid
Settings: When the filter value is not available: provide default value => Current OG group from context
Now, the fields portion of the view will relate to the base entity for the OG