Another related truth is that all sufficiently large applications begin to resemble an operating system. And so if you are developing a wiki, a blog server, or anything with the term "server" in it, and you find yourself adding "plugin"-like capabilities, you could do worse than to understand Minix 3, especially with respect to reliability. Well, and Erlang, etc.
Actually, what should be on the reading list? One of the first I had to read was on the THE operating system.