Mac: Sometimes, cut, copy and paste aren't really enough. If you'd prefer to swap out text instead, developer Peter Ellis Jones shares his Automator workflow for adding a "swap" function.
The basic idea here is that this workflow adds in the ability to swap one bit of text of another. You cut the text you select and replace it with what's currently on the clipboard, and the original text is then put on the clipboard. It's a pretty helpful little workflow if you work with text a lot. Head over to Jones' site for the full installation instructions.