Father of the web Tim Berners-Lee is working on a new project called Tabulator: "the generic data browser which lets you do useful things with your RDF data the moment it's on the web." In his post this week Slicing and dicing web data with Tabulator he includes some screen shots including data browsing and an auto-generated Google Maps mashup. It can essentially get you code-free mashups.
It works by exploring the web of relationship between things, loading more data from the web as you go. Then, if you find a pattern of information you are interested in, it will search for all occurrences of that pattern and display them in tables, maps, calendars, and so on.
Think of all the different mash-ups people have made for putting things like friends houses, photos, or coffee shops on the web. Each a different mash-up for a different data source.
For data in RDF (or any XML with a GRDDL profile), though, then you don't have to program anything. You can just explore it and map it. And you can map many different data sources at the same time.