Yes, and we have paying customers. We're working on some in-depth case studies, but until then, here are some quotes you may be interested in:
This allows FoundationDB's core ordered key-value data model to be used to expose many different data models (graph, document, even SQL) through stateless "layers". Users can then interact with their data through whichever data model makes sense for the application, but with a common, highly performant and reliable underlying storage technology. Another benefit of having just one storage technology, with ACID transactions, is that updates can be made with perfect consistency to multiple data models (i.e. update a document and a graph) with one operation.