Tom, I love this little hint. It is very hard for students to find the big idea given that they are novices in the new domain (if they weren't, why would they need teaching? :o) By definition and from research we know that novices in a domain have trouble finding salient points quickly whereas experts are defined by being able to see things that novices cannot. Have you ever noticed this in yourself when you are learning something new? (for example, these new tech tools! :o) I think Diigo has lots of potential to be a great "just-in-time" support for students. What do you think?