I can see the potential of mashups using tools like Googlemaps. They are an extension of past methods of creating new documents and applications by amalgating various online tools, but in a more sophisticated way.
From my own personal perspective I can see it being useful in creating such things as maps linked to photographs and descriptions of places I've been to and would like others to know about. Adding a bit of music or dialogue could make it even more interesting. The potential is unlimited.
Before I can create anything that ambitious I will need a lot of practice first.