I upgraded to OS X 1.4.9 yesterday. Now when I come back to my computer I cannot get out of the screen saver. Press many keys, click mouse ...etc. I have to press RESET button and restart the computer to get functionality back.
In the ByHost folder within your Preferences folder, there should be a file named com.apple.screensaver.XXX.plist where XXX is a bunch of random numbers. Drag this to the Desktop, restart and see if the problem reoccurs. You'll have to reconfigure your screen saver settings though. Is your screen saver set to ask for your password when you wake it?