This is definitely something I am working toward with my students right now (using Google Docs and Teacherblogit.com). I think it makes so much sense to move away from the traditional pen-and-paper feedback as instructional practices are already evolving past that. The hyperlink provided some great feedback ideas as well; the author used Audacity to "voice grade" essays, and also explained how to give audio feedback in Google Docs. Just imagining how much more efficient and thoughtful feedback could be for the students using these methods is exciting to me. The only thing I would look for is a way to transcribe the audio feedback for students who also like to have something written in front of them.