Let’s say I want to disappear from Facebook without completely deleting the account (in case I want to keep my contacts, for example, or the content I have uploaded to the service). What steps should I follow to conceal my account as much as possible without having to remove it?
Go to http://www.facebook.com/deactivate.php. Your account will be suspended and not be displayed to others in any way, but you can always re-enable it by simply logging in again.
You will not lose any data, everything you entered as well as your list of friends and all application settings are preserved.
As stated in the FAQ:
There is a setting to do this.