I discovered the hard way that a few of the screen savers that come with OS X actually crash (at least on my machine) which means just trying to select them in "Desktop & Screen Saver" crashes System Preferences. If you're unlucky enough to have System Preferences save the selection before it crashes (as I was), that means your screen saver will not work, and you cannot change it because each time you try, System Preferences will crash. Bad situation.
The fix, I discovered after some trial and error, is to:
- Open the terminal.
- cd into ~/Library/Preferences/ByHost.
- rm com.apple.screensaver.*.plist.
For extra credit, you can just remove the relevant plist file with the newest modification date which will reflect the moment you got yourself into this mess.
As a side note, I actually don't even like screen savers, and prefer to use the "Energy Saver" option to simply turn off my display(s). The problem, however, is that you can't configure OS X to require a password when the displays come back on. If you want to protect your workstation while you're away, you have to configure your screen saver to activate at a shorter interval than your displays turn off.
Dear Apple: please add a password option to turning off displays so we can be energy conscious and security conscious at the same time.