Set icon size equal to panel height
In Lubuntu, the shutdown button is in the bottom-right of the screen. From a usability standpoint, you should be able to "throw" the cursor to the bottom-right and be able to select the button -- this makes it easier to hit the button because you can move the cursor infinitely to the right and/or down and still be able to select the button.
However, the icon's size (22px) is smaller than the size of the panel (24px), so there are 2 px of empty space along the bottom of the button. That means you have to move the cursor exactly. However, changing the icon size in Panel Preferences to equal the panel size puts the button flush with the bottom of the screen, making it infinitely easier to select the shutdown button.
DistroRelease: Ubuntu 11.10
Package: lxpanel 0.5.7-0ubuntu1
Uname: Linux 3.0.0-8-generic i686
Date: Wed Aug 10 12:39:14 2011
InstallationMedia: Lubuntu 11.10 "Oneiric Ocelot" - Alpha i386 (20110801)
UpgradeStatus: No upgrade log present (probably fresh install)