In Konfabulator 1.5.6, Desktop level widgets are excluded from Exposé. However, some widgets cannot be used in Desktop mode (e.g., Desktop Changer) and thus cannot be left out of Exposé ... or can they? I accidentally discovered that if you choose the Desktop level, close the widget preferences, and then open them again and change the widget's level to Below, the widget remains in its place when invoking Exposé!
Most probably this behaviour is a bug in Konfabulator, because it changes back to the "normal behaviour" after rebooting.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040217000318955