Sometimes you want to send a file, URL, text snippet, or image from your Mac to your iPhone (or vice versa). I generally use email for this purpose, but Mac OS X Hints reader NaOH-Lye found another method (via MacDrifter): Use Messages.
If you have the Messages beta installed on your Mac, click on the Compose button at the upper left of the Messages window. At the To prompt, start typing your own name, then select your iMessage address from the list of suggestions. Then drag (or copy and paste) your file, URL, or text snippet into the text-entry field at the bottom of the window. Whatever you’re sending will appear on the “sent” side of the message pane; it will almost immediately appear in the “received” side, too. More importantly, it will almost immediately pop up on your iOS device as well.
This works in the other direction—from iOS to Mac—too, though it’s limited to text and images. For text, you obviously just type the text into the text-entry field. (This could be a handy way to take notes on your iPad, then send them quickly to your Mac.) For images, you tap on the camera icon, then select an existing image from your Camera Roll or photo library. This could be particularly useful if (like me) you have to take screenshots on your phone or tablet and send them to your Mac; it’s way easier than doing so via email.