Many of us spend a lot of our time at our computers. Yet how efficiently do we really use them? Memorizing the most useful keyboard commands might save you minutes a day. Here are some of the most useful ones I've found: Switch windows within a single application (Command-` on Mac)Paste while using the formatting of the document you're pasting into (Command-Option-Shift-V on Mac)Skip to next/previous email in the Gmail email client (k and j once you turn on Gmail key commands)Show desktop (F...