Yahoo: Mail integrated with Messenger

Yahoo!Mail beta has integrated with Messenger. Specific functionality:

• Presence awareness - when the recipient comes online, it notifies you during composition
• Switch comm - Instantly move an email composition into a messenger conversation
• Group join - allow others to join and view the message thread (I think)

It seems to be limited to Yahoo Messenger, which I don't have, so I couldn't try it first hand. MSN Messenger is supposed to be integrated with Yahoo, but apparently not for this functionality. Ryan Kennedy created a nice little video demo of the email-messenger functionality.