I'm guessing that whoever got offended at being called 'amateur' was equating the term with 'not being good/experienced enough to be a professional'. I've seen plenty of stories about self-centered people who were supposedly paid to know something, only to be outfoxed by unpaid hackers who would not pass an interview, but actually know a thing or two. Makes you wonder who's the one with professional-grade knowledge.
Back to the topic... I guess you could say that FreeBSD is a hobby for me. Not even so much the kernel/userland/CLI, but rather, the fact that it forms a VERY solid base for stuff like KDE and networking, while keeping things simple, and consistent. I guess a good analogy would be a rocket launchpad - I'm more interested in the rocket than the launchpad, in all honesty, but for a successful launch, you gotta invest in the launchpad first, and that's what I'm doing with FreeBSD, after getting frustrated with Linux.