The Apache Software Foundation (you might have heard of them ;) runs their servers on FreeBSD.
NetFlix runs some (all?) of their servers on FreeBSD.
Google uses FreeBSD for their network search applicance (for corporate intranets or whatever). They also just announced their funding of the Capsicum security framework project for FreeBSD (and later, a port to Linux).
The Weather Channel uses FreeBSD to power their network appliances that render the forecasts for local cable networks.
NetApp and Juniper Networks use FreeBSD for their networking gear.
There are more examples here if you want to read them:
The FreeBSD forums are reasonably active and very friendly, you should check them out if you want to learn more (or have more questions about *BSDs in general):
Also, Netflix and Yahoo are pretty big users. I used to use BSD on my personal machines just because I prefer their approach to things and the documentation. I now use Linux just because my day job practically requires it.
edit: And regarding GP's surprise about Mandriva - Mageia is a community fork and is #2 - the Mandrake users I knew all switched to Mageia.
To add to that list, there's also pfsense: http://www.pfsense.org/ a FreeBSD based distribution for building routers which uses the pf firewall, originally from OpenBSD. I know a number of small companies, my own included, which use it and there's even a book written about it!
I'd hazard a guess that there are similar projects based on BSD floating around for various other uses too.
NetFlix runs some (all?) of their servers on FreeBSD.
Google uses FreeBSD for their network search applicance (for corporate intranets or whatever). They also just announced their funding of the Capsicum security framework project for FreeBSD (and later, a port to Linux).
The Weather Channel uses FreeBSD to power their network appliances that render the forecasts for local cable networks.
NetApp and Juniper Networks use FreeBSD for their networking gear.
There are more examples here if you want to read them:
http://www.freebsdfoundation.org/testimonials
The FreeBSD Foundation also has a list of donors:
http://www.freebsdfoundation.org/donate/sponsors
The FreeBSD forums are reasonably active and very friendly, you should check them out if you want to learn more (or have more questions about *BSDs in general):
http://forums.freebsd.org/
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EDIT: I forgot one; VeriSign apparently uses FreeBSD enough that they just started their own BSD-related conference:
http://lists.freebsd.org/pipermail/freebsd-questions/2013-Ap...