Terminal Commands for Hidden Settings in Leopard
In general, these will only work with Leopard
For the most part, applications will need restarting before changes take place. For the Dock and the Finder, it isn't obvious how to do this. The easiest way is to type a second command into the Terminal afterwards. Type "killall Dock" followed by return for all the Spaces, Stacks and Dock commands. "killall Finder" followed by return for all the Finder related ones.
Spaces
defaults write com.apple.dock workspaces-edge-delay -float 0.5Changes the delay when dragging windows off the edge of the screen to other spaces. Default value is 0.75.
defaults write com.apple.dock workspaces-wrap-arrows -boolean NODisables the wrap-around when using Control-Arrow keys to changes Spaces. To enable again, repeat with YES at the end.

Stacks
defaults write com.apple.dock persistent-others -array-add '{ "tile-data" = { "list-type" = 1; }; "tile-type" = "recents-tile"; }'Creates a Recent Applications stack in your Dock, that you can change to display other recent items. To remove it, use the command defaults delete com.apple.dock persistent-others but be warned, this will remove all your stacks.

defaults write com.apple.dock mouse-over-hilte-stack -boolean YESAdds a Mouse Over gradient to items in your stacks. To disable, repeat with NO at the end.
Dock
defaults write com.apple.dock no-glass -boolean YESChange to 2D Dock. To change back to 3D, prepeat with NO at the end.
defaults write com.apple.dock tilesize -int 256Allows you to increase the size of the Dock past the maximum allowed by the slider in System Preferences. Don't go larger than 256. Use the slider in System Preferences to shrink the Dock down again.
defaults write com.apple.dock largesize -int 512Allows you to increase the Dock magnification past the maximum allowed by the slider in System Preferences. Don't go larger than 512. Use the slider in System Preferences to shrink the Dock down again.
defaults write com.apple.dock enable-spring-load-actions-on-all-items -boolean YES
Makes all items in the Dock spring loaded. For example, hold a file over an application and it will open or come to the front so you can drop the file onto a specific window. Repeat with NO to reverse.
Finderdefaults write com.apple.finder FXListViewStripes -bool FALSE
Removes the stripes in list view. Repeat the command with TRUE to reverse./System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -domain local -domain system -domain user
Resets the "Open With" menu, clearing duplicates. The command is different from the one in Tiger.defaults write com.apple.finder _FXShowPosixPathInTitle -bool YES
Changes the title of a window to its full path. Repeat with NO to reverse.
Spotlight
sudo chmod 0 /System/Library/CoreServices/Spotlight.appDisables the Spotlight icon. Type "killall Spotlight" for changes to take effect. To re-enable it, type 755 instead of 0.
Time Machine
sudo defaults write /System/Library/LaunchDaemons/com.apple.backupd-auto StartInterval -int 7200Changes Time Machine's backup interval. Requires an administrator password. Default value is 3600 (seconds).
iCal
defaults write com.apple.iCal IncludeDebugMenu YESEnables the Debug menu in iCal, just like the Safari one. Repeat with NO at the end to disable.
Safari
defaults write com.apple.Safari DebugConfirmTossingUnsubmittedFormText NODisables the warning given when closing a window with text entered into a form that you haven't submitted. To bring back the warning, repeat the command with YES.
Check out this article for more Safari 3 tips.
Menubar
Changing the menubar will require an administrator password and you will need to restart the Mac for changes to take effect.
sudo defaults write /System/Library/LaunchDaemons/com.apple.WindowServer 'EnvironmentVariables' -dict 'CI_NO_BACKGROUND_IMAGE' 1Remove translucency in menubar, turns it white.
sudo defaults write /System/Library/LaunchDaemons/com.apple.WindowServer 'EnvironmentVariables' -dict 'CI_NO_BACKGROUND_IMAGE' 0Removes translucency in menubar, turns it grey.
sudo defaults delete /System/Library/LaunchDaemons/com.apple.WindowServer 'EnvironmentVariables'Reverts back to default translucent menubar.
All Applications
defaults write -g PMPrintingExpandedStateForPrint -bool TRUEApplications use the expanded Print dialog by default. Similar to the expanded Save dialog in earlier OS versions. Repeat with FALSE to reverse.
If you're out to prevent an attack - not the computer type of hacks that are gained via a network, but the type that happen against your home or business, then consider a security system of some sort. Security Cameras these days can even be installed directly onto your computer which allow you to display and capture video or take photo's of all activity whether you're present or away.

