While Mac OS X 10.6.8 resolves numerous security vulnerabilities for Snow Leopard users, those still using Mac OS X 10.5 Leopard should download and install Security Update 2011-004. The most important fix is to AirPort, and it prevents an attacker on the same Wi-Fi network from causing your Mac to reboot. Other affected aspects of Mac OS X include ColorSync, CoreGraphics, ImageIO, MySQL, patch, Samba, servermgrd, and Subversion. Separate standalone updates are available for Leopard and Leopard Server, though it’s still easiest to let Software Update do its thing. (Free; 256.4 MB, 499.8 MB)
Option-click to Hide Apps Quickly
This trick has been available in the Mac OS for years, but many people still don't know it. If you have too many windows cluttering up your screen, you can hide specific ones easily as you work. When you're in any application, hold down the Option key and click on another app's window, on the Dock, or in the Finder to switch to that other app and simultaneously hide all the windows in the previously current app.
Security Update 2011-004 (Leopard/Leopard Server)
Set up short abbreviations which expand to larger bits of text,
such as "Tx" for "TextExpander". With the new custom keyboard,
you can expand abbreviations in any app, including Safari and