I'm not a professional system administrator, although my original jack-of-all-trades position at Smartleaf did include some system administration, and just about everyone at the MIT AI Lab got in on the act while I was there.
I do use many Unix-like systems on a daily basis, and maintain Linux, FreeBSD, NetBSD, and OpenBSD boxes of my own and for others.
Being a cheap bastard, I frequently find myself wedging Unix-like systems into small spaces. See my laptop, for example.
I've discovered that BSD systems need more memory than Linux systems at the very low end (4-12MB). Obviously, in this range, you have to strip the system down completely to make it usable. Compiling custom kernels helps BSD quite a bit, of course.
I tried to switch my wireless network from routing to Proxy ARP bridging with limited success.
Sometimes, you just need a pile of modems. (I still have them. If you need them, make me an offer that will pay for shipping and I'll probably sell them to you.)
I had pretty good luck turning a Pentium 60 box with 24MB RAM into an Internet appliance for my in-laws. I ran Debian Linux on it and set up a PPP attack dialer so you could just turn the modem on or off to get in on or off the Internet. I administered it remotely.
The only real problem I had with this box being so small and slow was Netscape. It was a little too slow for my in-laws and it tended to consume resources even when it wasn't being used. With each of my parents in law running Netscape under KDE in a virtual console, this was just too much for the poor little computer.
-- Peter Szilagyi <szilagyi@alum.mit.edu>; revision: 1.14, Tue Feb 9 18:10:16 2010