Kevin Walker is using a very interesting concept, which he calls "learning trails":
This research explores the hypothesis that having a trail of where you have been - or creating a trail for someone else - helps you to learn.Your web browser keeps a history of the pages you visit. What if you had a record of the artifacts you saw on a museum visit? Or sites in a foreign city? It is hypothesized that in any unstructured or semi-structured knowledge base, trails help to filter and connect individual 'learning objects' by providing a linear, narrative structure. I test this in the real world, with technology for automatic capturing of trail data, and by enabling people to easily create learning trails for other people. (...) The value of an automatically generated trail is in the way it is represented after it is created - when it can be revisited, edited, and shared - thus I call it a 'reflective trail.' If, however, you consciously create a trail for someone else, its value to the other person is in its use by them. But there is an added value to you, the creator, because consciously creating a trail requires planning and thought about what story the trail will tell, and how each stop will contribute.
Why do I blog this? I like this idea of using trails to afford specific behavior (this can be articulated to the "social navigation" concept), which eventually would be interesting for various purposes (learning activities, signalization in public transports...)