Google has added a new feature across its Google Docs products called Discussions to facilitate faster and better collaboration.
Google's current system for making comments on documents has been relatively haphazard until Discussions. Word processor documents could only have minor commenting and Google Spreadsheets had a chat system that didn't include notifications.
Google's new system allows users to comment directly on specific points of the document and start a discussion about it. Once the discussion is resolved, an owner / editor of the document can close the comment and resolve it in the system. Notifications of comments are sent via email, which makes getting notifications about new comments fairly simple.
You can even invite someone to make comments by using the @mention system Google has developed. This allows you to search Gmail for any mentions along with sending messages. Take a look at the video below of it in action.
Google Discussions In Action
You can read more about the new feautre and see additional screen shots on the Google Docs' Blog.