Any one who has used a Windows computer knows about using the “three-finger” salute — Ctrl-Alt-Delete — brings up a dialog where you can quickly start the screen saver. Provided the screen saver option is configured to require a password the computer can be locked with a minimum of fuss.
Mac OS X doesn’t provide a simple keyboard shortcut to activate the screen saver and lock the computer. On MacBook laptops you can press the power button briefly which brings up a dialog allowing you to Restart, Sleep, or Shutdown the computer. The sleep option can be selected just by pressing the “S” key.
Recently I discovered that Alfred can be used to activate the screen saver. And, just like on Windows, if the screen saver is configured to require a password to wake the computer, you can lock the computer this way.
My Alfred is set up be activated with Cmd-Space. Once the Alfred dialog is displayed typing “sc” is enough to select “Screen Saver” from the list of matches. So, Cmd-Space, “sc”, and then pressing the “Enter” key activate the screen saver. I find this keystroke combination particularly useful on the iMac I have at work, especially when leaving my desk for few minutes.
Oh, and I recommend downloading Alfred from their web site rather then using the Mac App store as the App store version tends to lag behind in releases.