I teach economics at the college level. I require my students to send me their papers digitally. I don't require pdf because I can convert the file if they don't. I use the annotate feature to mark up their papers just like a piece of paper and email it back to them when I'm done. For longer term projects, having that record of what you told them to do on their last draft is incredibly helpful.

I have also used the projector to write and draw during class and have the class notes available for students. There are some issues with the projector app but I know they are working on those issues.

Also, someone mentioned having issues with staying organized with the tags. I use my syllabus and attach all the related files. This is a much easier way to keep track of everything for one class, in addition to the tags.