If your computer seems to have crashed or frozen up, or is taking WAY too long to finish doing some task that it won't let you interrupt, press Command-Option-Escape. This will sometimes bring up a dialog that reads "Force 'application' to quit? Unsaved changes will be lost." The dialog has two buttons, "Force Quit" and "Cancel". Sometimes, clicking on "Force Quit" will kill the active application, allowing you to continue using your Mac without having to restart. Take advantage of this to save your other work and restart your Mac as soon as you can, because a crashed application might have trashed other things in memory. Use this at your own risk! Sometimes it won't work, but if your machine's hung, it could come in handy.
