If you're working on a document and you want to send it to a friend/colleague as an email attachment, you probably know that you can drag the actual file icon to the Mail icon in the Dock to create a new message containing that file. But to do this, you have to navigate to the Finder and find the file.
Another way to do this is to save your work, click the proxy icon in the title bar (the small icon next to the file's name) and drag it onto the Mail icon in the dock. This creates a new message with the working document attached to the message.
Make sure you save the current document; otherwise the icon in the window title is dimmed and cannot be moved.
You can do this with web pages in Safari or Firefox (and perhaps in other browsers) by dragging the icon to the left of the URL in the address bar; in this case, the current URL is pasted in the body of the newly created message. If, however, you are viewing a local file, it's that file itself that will be added to the message.
Note that any changes you make to your file after adding it to a new message will not be reflected in that attachment; the file is added to the message in its state at the time you drag it.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20061025131738810