Here's something I found is quite useful. If you tell your computer to shut down, and then remember you forgot to do something (send an email, or check weather, or what have you), wouldn't it be nice if you could stop that shut down process, so that you could then handle your forgotten task without having to go through the full power-up process?
One good way to stop the computer from quitting all applications and proceeding to shut down is to click on any non-running application in the Dock (preferably one that will take more than one bounce to open), and that process will then cancel the shutdown routine. Hope this helps some folk out there.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060806011748864