You can drag text into the dock and do a variety of things with it.
For example, if there is a piece of text you want to email a friend, don’t bother copying and pasting, just highlight the text and drag it to the Mail icon. A new message will pop up with the text ready to email.
This same trick works with other applications as well. Drag some text into the Safari icon and it will perform a Google search for you. Or you can drag the text into Text Edit for instant copy and pasting.