Mac users switching from Windows or Linux learn quickly to substitute Command for Ctrl. Command+C copies text to the clipboard, for example, although Ctrl+C does the same within Windows and Linux GUIs.
However, Ctrl isn’t just another modifier key on a Mac keyboard. It can be used when typing for a handful of interesting editing tricks that it’s worth trying to integrate with your workflow. See below.
Note that the secret secondary clipboard mentioned below is a basic clipboard that can store only plain text and is independent of the main OS X clipboard.
Ctrl+A: Jump to the start of the paragraph/line.
Ctrl+E: Jump to the end of the paragraph/line.
Ctrl+O: Insert a new line at cursor point, but leave the cursor where it is.
Ctrl+T: Swap characters on the left and right of cursor (a.k.a. transpose text).
Ctrl+V: Jump to end of document, although in some apps you’ll jump to the end minus one character (hard to explain — just try it in TextEdit and see what happens.); hit again to move to the actual end of the document.
Ctrl+K: Delete text from cursor point to end of paragraph/line (actually, it will store it in the secret secondary clipboard) OR if a word/sentence/paragraph is selected, cut it and place it on the secret secondary clipboard.
Ctrl+Y: Paste from the secret secondary clipboard anything cut using Ctrl+K.
Note that there are several versions of this list floating around the Internet but this one is correct for OS X Mountain Lion according to my tests. Before anybody points it out, yes, I know this is a subset of the Emacs command keys and, no, other Emacs key combos don’t appear to work in OS X.