There are different philosophies for hostname conventions. In my experience, using a common theme and context adds logic to a potentially complicated network.
At home, I use spells from old Infocom interactive fiction games as my naming convention. While it may seem silly, my home network is small enough that I can remember the purpose of machines, and I've got a large corpus of potential names. I've also seen others use names of characters from television, movies or books. Use your imagination!
At work or in a shared environment, I use more descriptive names, such as web-dev-01 for a development web server. Security through obscurity causes more headaches than it's worth as it makes it more difficult for others to understand the layout, and the illusion of security that comes from giving a machine a wacky name will not protect you from malicious users.
Either way, once you've developed a schema, stick with it; mixing naming conventions just makes things more difficult.