Google Inc. (NASDAQ:GOOG) has announced that discussions have been added to Google Docs. The discussions are rapid and seamless with e-mail integration. The discussion flow has ownership and edit rights to individual comments.
Each comment has a timestamp and a profile picture. You can add someone to a discussion using an @mention (example: @firstname.lastname@example.org). This would send me a message in my inbox with the question or comment. And my reply would show up in the document. To disable e-mail notifications for a document, you just have to select “Mute updates from this comment” at the bottom of any e-mail.
[Google Docs Blog]