I have a smoothwall for my network router/firewall. I've been happy with it, I've been using Smoothwall for about 6 years now. There isn't much to it since it is designed to be a network appliance. There are tons of mods for it though if you check out their forums.
On my servers and HTPCs I run Gentoo, I like the high degree of customization. The machines only run the exact software needed for their purpose and those packages only have the features in them that I need.