When most PC users talk about security, the first thing to come to mind is network/Internet security. On the Linux side, we turn off telnet, set up firewalls, disable unnecessary services, and so forth.
However, we rarely think about local security. For office workstations (and even home users), this is at least as important as protecting the system from the network, at least from accidental damage if not from prying eyes.
This Linux.com article by Joe Bolin provides a good start, outlining simple things like locking down the BIOS to keep out live CD’s as well as explaining how to lock down single-user mode and your boot loaders.