If you use Diigo but are researching a certain topic for a book or term paper and also use Evernote, I recommend setting up an ifttt.com recipe similar to this one I'm using for my collaborative writing book. Everything tagged "collaborative writing" goes automatically to my collaborative writing book.
You could use this for a course. You could take everything on Diigo tagged with the course number into a notebook (or into a Google spreadsheet, for that matter.) There are many other sources of information you can use to collect information on a topic in one place.
term.ly is the companion website for the terminology app for the ipad/ iphone. You can also shorten and share definitions. The main problem I had is if you use a diigo box, the search box tries to take over the words. Nice clean dictionary.