Google is organizing more and more things in its index based upon entity numbers. I have a couple of examples for you that show how they are being used.
It’s possible that you may have missed a reference to Freebase Entities in a Google Research Blog post from 2013. I missed it myself. The post is
Improving Photo Search: A Step Across the Semantic Gap.
In the post, the author (Chuck Rosenberg) tells us how they improve image searching at Google by labeling images with entities, rather than text strings. The entities they used are entities that you would find at a source such as Freebase. He tells us that they use Freebase Machine ID numbers for those labels:
As in ImageNet, the classes were not text strings, but are entities, in our case we use Freebase entities which form the basis of the Knowledge Graph used in Google search. An entity is a way to uniquely identify something in a language-independent way. In English when we encounter the word “jaguar”, it is hard to determine if it represents the animal or the car manufacturer. Entities assign a unique ID to each, removing that ambiguity, in this case “/m/0449” for the former and “/m/012×34” for the latter.