Communicate Coughing -- If you try the Communicate Lite demo mentioned in TidBITS #199, and you leave it connected but idle in the background, it will make a slight coughing noise every five minutes to let you know you are still connected, much as AppleLink does. The reminder helps you to avoid running up a phone bill or running down a PowerBook battery. If you don't like the sound, you can turn it off, pick another one, or increase the time between reminders.
Sleep (and Lock) Your Screen
When you are walking away from your computer, it's fairly common practice to start your screen saver and lock your screen. But did you know that there is a built-in keyboard shortcut in Mac OS X to sleep the screen?
Press Control-Shift-Eject and your monitor sleeps without engaging the screen saver.