Since I hate lifting my hands off my keyboard to click on a mouse when I don't have to, I use keystrokes to save time (which adds up if you're on the computer for 8 hours a day!). Someone was just asking me about them, so here are some links to the ones I most frequently use (hopefully this his helpful, but I apologize if this is confusing):
This one is probably the most useful, which I use all the time:
click "Alt" + "Tab" to switch between two programs ("Command" + "Tab" on Macs).
If you wanted to get fancy, hold down "Alt" and click on "Tab" ("Command" then "Tab" on Mac) and you can scroll through all your open programs, stopping on the one you want; hold "Alt, Shift" then "Tab" to go in reverse.
If you're using Windows Vista or 7, click the "~Windowsbutton~" + "Tab" and you get a super fancy way to scroll through scroll through your open programs; hold "~Windowsbutton~", Shift" then "Tab" to go in reverse. (the "~Windowsbutton~" is that one to the left of the "Alt" button)
Of course, "Ctrl" + "X" to "cut"; or "Ctrl" + "C" to "copy"; or "Ctrl" + "V" to "paste" are incredibly useful and efficient (Macs use "Command" instead of "Ctrl" ... or whatever that button is to the left of the space bar)
(All of these might be slightly different on Macs.)
Microsoft Word
http://support.microsoft.com/kb/290938
Firefox browser
http://support.mozilla.com/en-US/kb/Keyboard+shortcuts
Gmail
http://mail.google.com/support/bin/answer.py?hl=en&answer=6594
Also, most programs have their own shortcuts, which save a lot of time (I use them in AutoCAD, and all the Adobe programs ... InDesign, Photoshop, Illustrator; Google Sketch-up. Google Earth. Unfortunately, ArcGIS does not have any, yet).
