Yeah, it goes from people putting Prometheus on their Raspberry PI all the way to companies like DigitalOcean monitoring millions of machines with Prometheus (https://promcon.io/talks/scaling_to_a_million_machines_with_...).

A lot of open-source projects (Kubernetes, Etcd, ...) are also exposing native Prometheus metrics now, making it easier to integrate with those.

EDIT: also check the PromCon schedule for other user companies giving talks: https://promcon.io/schedule/

And the sponsors are also users: https://promcon.io/#our-sponsors