Comment 7 for bug 67391

Confirmed, if you kill kdesktop then restart it the screensaver begins to work. I found I had to put a sleep between the kill and restart like this: killall kdesktop;sleep 1;kdesktop&

The restart also gave me these errors which may or may not have any significance:
 X Error: BadDevice, invalid or uninitialized input device 168
  Major opcode: 145
  Minor opcode: 3
  Resource id: 0x0
Failed to open device
X Error: BadDevice, invalid or uninitialized input device 168
  Major opcode: 145
  Minor opcode: 3
  Resource id: 0x0
Failed to open device

By-the-way, I'm using a Lenovo 3000 N100 laptop.