One of the biggest problems when working with Humanities scholars (or scholars in other areas) is that they are accustomed to using the commenting features of their favored format (usually Word). Now, PDF has the facility to allow commenting. The only problem is that Adobe keeps the keys to this particular kingdom pretty tight. No open source PDF thing (other than PDFEdit, which isn't very stable from what I have read around the web) can add comments to a PDF in a graphical environment.
This brings us to closed source but free products that allow you to add comments graphically to a PDF. There are two that I know of and both work on Windows: Foxit Reader and PDF-XChange Viewer. Foxit has a free Linux version but it doesn't allow commenting yet. However, Foxit does work under Wine but I have not tried it yet.
This takes down one more barrier to adopting LaTeX in the humanities if you can get your University or supervisor to support an non-Adobe PDF reader.