Full screen application causes screen saver to not start (Lion) When I am in a Full Screen application mode, the screen saver doesn't start. So I have to shift to another screen that doesn't show a full screen app. There the screen saver starts!

This naturally happens only in Lion.
A workaround would be to assign a Hot Corner to start the screen saver. To do this, go to System Preferences &gt; Desktop &amp; Screen Saver &gt; Screen Saver &gt; Hot Corners… and select "Start Screen Saver" in the drop down menu of your choice.

(Side note: Hot Corners is also accessible from the Mission Control prefpane.)