View Own or the Community's Markups on a Document/e-book
Community interaction is wonderful! Especially if you have the option to toggle between seeing everyone's notes or just your own notes. Especially if there are several reviewers. Personally, I'd like to make a workbook available to my students, give a single URL, and each student could choose to see just their own markups on the Workbook, or that of the entire group (e.g., 12 students). To see an example of this, check out Bookglutton.com.
Robert Kelley commented
Note - With a reviewer login, would also help if people could only delete their own markups.