Well, really you talk and your comments get recorded into the Google Doc. Here is a video of how it works. It was created by a high school English running a paperless classroom, but the concept can be applied to anyone using Google Docs to collaborate. I already tried out the process to give feedback to a student, and the recording and playback worked perfectly for me. Now to try it out with more students and to see if this is concept that will spread to other classrooms. Let me know what you see as the possible application of voice recording into a Google Doc after you watch the video.