I think one could use depth of field in shooters too. Even there, there are conventions of "focussing", means pointing at things as usable or movable, normaly by giving them a white or reddish light. Why shouldn't we use depth of field for this?

http://www.puppenheim.org/
http://www.wuerfels-welt.de
Old Game Tutorial: http://www.puppenheim.org/MITutorial.zip
Free Game Editor: http://puppenheim.org/AlienalsWeihnachtsmann.zip
http://www.puppenheim.org/blender_starting_main_settings.txt