Success stories of PostgreSQL implementations in different companies

Even with that, some clients are being encouraged to change to PostgreSQL to lower their companies costs in technologies, but very often they ask if there are success stories of PostgreSQL implementations in companies in our region or around the world, success stories (if is possible) with some information like number of concurrent users, some hardware specs or storage size.

I think that in my country is more common to hear success stories like that about other databases like Oracle because is more expanded here, but i would like if there's a place or if you can share with me some real experiences or success stories that you ever heard of successful implementations of PostgreSQL in companies to talk with people when they ask that kind of things.

Regards.