I like this in principle, but I think you have two types of users you are trying to serve. There are people who want to annotate, so they need the "Add Tag" and "Add Annotation" items. I just want to read them like margin notes. I would rather not click into each one--particularly since there is enough space to show them all. Would be nice to reduce the complexity of reading a bit, even if it comes at the expense of making commenting a click or two away.