I briefly worked for a place that had been through cstore and greenplum before buying into Vertica, right before I started. They were simply hungry for analytical performance and had the cash. It was a really great buy for them in performance but also ease of use.
Hindsight: I was skeptical that they'd left all the metadata (configuration/application domain data) in PostgreSQL while moving the (100x larger) business data to Vertica. At this point I'd repeat the pattern just for the sheer delight of dealing with a complex application schema in PostgreSQL. The flexibility demanded of Vertica was decidedly less in that shop.
