Different to other release,the latest version of ubuntu Jaunty has a confirm dialog within 60 sec. when you logout,shutdown or restart. It prevents anyone to make a mistake,but anyway it may be excrescent for some people and there is a easy way to disable it.
Right mouse click on the Switch users or shutdown area at right top,click Preferences
You will see following screen,unmark the line which says “Show confirm dialogs for logout,restart and shutdown”and then close it,just so easy.
For ubuntu 9.10,read here.