Script Summary: Minimize GMail Header, Nav Bar or Ads. Used to be called "GMail Header, Navigation and Ads Switcher"
Can switch(hide/show) the header, navigation bar and ads by clicking the triangle icon on top,left or right respectively. It effectively maximizes screen real estate for information you consider important. I typically hide all 3 to max message space.
The original code written for Google Calendar is http://userscripts.org/scripts/show/8507 by margin. I found margin's calendar version very helpful so I applied it to GMail.
Version 2.0.2 01/28/2008 - workarounds/fixes for new GMail update
Version 2.0.1 11/30/2007 - update for new GMail layout that cause a few problems
Version 2.0 11/11/2007
+ Updated for New GMail