My reaction was, It’s cute how the bars move but why is this the future?
Integrated in the browser, works on any device, requires no software
installation. Here are more examples, for maps.
I just saw a practical application of d3.js used to establish network diagrams of organizations tracking your browsing history. Here's the introduction . . .
. . . and here's the guided tour of the application:
It's the future of "presentation" visualisation. Important to make the distinction of between exploratory and expository visualisation. D3 is fantastic for exposition, but fails miserably for exploration because it lacks the all of the other tools (e.g. models and data manipulation) needed for good data analysis.
D3 isn't so much a visualization system (in the infovis sense) as a platform for building visualization systems; I think of it as a visualization kernel rather than a framework. So you're right that the core library (as small as it is) isn't good for exploratory analysis—it isn't designed to be. Instead, you'd build exploratory tools and models and data manipulation on top of D3. D3 doesn't dictate a particular way of visualizing, but provides a useful foundation that handles the display, object constancy, transitions, etc., so you can build more powerful tools on top of it.