Very interesting thread. I hope people actually do come into the discussion. It'd be really interesting to see some real-world experience.
My work doesn't entail full Linux or network administration, although that is something I would like. All production platforms at work are FreeBSD. Similar to ... but yet not Linux. Linux is more of a hobby for me ... something I like experimenting in. Some I use for my own dev/fun servers. I'm not an expert Linux user nor am I forced to learn it because of work ... so I think that keeps it fresh and always fun for me.