If you friend coworkers without creating separate accounts, you might find it helpful to subdivide your friends into friend lists. Friend lists allow you to set different privacy levels for different groups, which enables you to be a bit more selective about which portions of your profile are visible to whom.
Friend lists are also useful for appearing offline to people that are constantly trying to initiate chat with you -- a huge drain on time and energy. Simply create a special friend list and then set the chat window slider to "go offline." It gets you off the hook without bruising anybody's feelings (but if they hunt you down in your cube, you're on your own).
You can also customize who sees (or does not see) your News Feed posts. Below the text box, on the right-hand side, next to the "share" button, there's a pull-down menu with a padlock icon. Using this, you can set your post to be visible to "everyone," "friends and networks," "friends of friends" or "friends only." You can also customize each post to be visible to specific people, specific networks or to yourself alone. You can even remove individual recipients. Remember: Anything you share with "everyone" can be seen by anyone on the internet -- not just anyone on Facebook.
On a related note, think carefully before changing your status to "in a relationship" with someone in the office, unless you want it known by everyone (and are ready for the potential Facebook fallout following a breakup).