Starting up in Safe Mode on a Mac

These instructions were taken from a couple of help articles on the Apple site.

Starting up in "safe mode" may help you diagnose problems you're having with your computer.

To start up in safe mode:
1) Shutdown your computer and wait 10 seconds.
2) Press the power button.
3) Immediately after you hear the startup tone, hold down the Shift key. You should press the Shift key as soon as possible after you hear the startup tone, but not before.
4) Release the Shift key when you see the gray Apple logo and progress indicator (spinning gear).

To leave safe mode, restart the computer normally without holding down any keys during startup.

What does Safe Mode do:
1) It forces a directory check of the startup volume.
2) It loads only required kernel extensions (some of the items in /System/Library/Extensions)
3) It disables all fonts other than those in /System/Library/Fonts.
4) It moves to the Trash all font caches normally stored in /Library/Caches/com.apple.ATS(uid)/, where (uid) is a user ID number such as 501
5) It disables all startup items and logins items.
6) A Safe Boot deletes the dynamic loader shared cache at (/var/db/dyld/). A cache with issues may cause a blue screen on startup, particularly after a Software Update. Restarting normally recreates this cache.

Taken together, these changes can help resolve software or directory issues that may exist on the startup volume.

Some features may not work in Safe Mode:
1) DVD Player, capturing video in iMovie, audio input or output device
2) Quartz Extreme (hardware accelerated graphics) is disabled. Any applications dependent on this will not work.
3) In Snow Leopard, File Sharing access is disabled. This means you will not be able to mount Time Capsule or any volumes being served by other Macs.