The Competitive Edge Explorer is a mapping project from the MIT Laboratory for Mobile Learning. It's not just some hodge podge Google Maps mashup. The Explorer was written in Processing and has an intuitive and responsive user interface. As the user switches through datasets or zooms in and out, the map changes instantly. A total of eight datasets, including education, income levels, and housing costs, are available and can be selected at the same time to compare different areas according to different variables. The Explorer is yet another example for how maps offer the user a familiar visualization (just like timelines) for data.
It would be especially cool if the Explorer was not just for Boston, but for the entire U.S. or even better, the world. Of course, finding that much data seems impossible now, but hey, it doesn't hurt to hope.