The experience David describes in "The Right-Time Web" broadly fits in the "context -aware computing" arena – the intersection of where you have been, where you are, where you will be and when, and the topical/semantic context around each spatio-temporal location and your activity there and the intersection of those things with others both socially and professionally as David describes in his examples.
Historically, context-aware computing has been limited by our ability to have sensing and computing with the user at all times. Today we are way beyond that, with our Smartphone devces bristling with sensor technology and plenty of computing power.
What is missing is a framework in which to establish measurements of relevance. I don’t mean your grandpa’s Information Retrieval-based view of search result relevance, I mean a measure of "this gets me/us and makes sense, right now". At the heart of enabling this, I believe, will be systems that can jointly reason with both physical and semantic attributes, dates, times and coordinates, in addition to the pertinent topic-based semantics – watch this space!