My name is Linus, and I am your God. — Linus Torvalds
Is Linux an operating system? No, but I’ll leave the holy war to Richard Stallman. For my intents and purposes it will serve just fine to not make a distinction. Where I will make a distinction is between RedHat and Debian derived systems (and maybe Slackware if you really want me to). I’ve worked on them all in a server and some in a desktop environment; from eight core beasts down to diskless embedded devices.
I have designed mass installation and configuration systems and used some third party ones like cfEngine. I have a body of experience dealing with RPMs and their creation and modification, including work with yum and cached repositories to save bandwidth. My weapon of choice is vim and the CLI.
Linux is awesome as network glue. I have taken machines as ancient as 486s and Pentium 100s and turned them into respectable firewalls and routers. Recycling and repurposing old hardware into new and useful tasks is bordering on sublime in my mind. Not always a good practice on a network that you need reliability, it can be a powerful cost savings and emergency duct tape nonetheless.
In the majority I have used Linux as a webserver. Other projects have included a file server that authenticated to Active Directory on a website as well as on a local network. I have successfully deployed both MySQL and PostgreSQL to good effect on Linux.