The Layouts tab in the keyboard preferences dialog does not have any tooltips. Adding them will make the the dialog easier to understand.

Here are some suggestions for strings to use for the tooltips:

Layout list -> 'List of keyboard layouts selected for usage'
'Add...'  button -> 'Select a keyboard layout to be added to the list'
'Remove' -> 'Remove the selected keyboard layout from the list'
'Move up' -> 'Move the selected keyboard layout up in the list'
'Move down' -> 'Move the selected keyboard layout down in the list'
'Print' -> 'Print a diagram of the selected keyboard layout'
'Options...' -> 'View and edit keyboard layout options'
'Reset to defaults' -> 'Replace the current keyboard layout settings with the default settings'

This bug is part of the keyboard preferences design review which can be found here: http://live.gnome.org/UsabilityProject/Whiteboard/KeyboardPreferences