The NY Times has an interesting article about mashups - Do the Mash (Even if You Don't Know All the Steps)
"POP music has its mash-ups that combine tunes and vocals from different songs. YouTube viewers do it, too, mixing together segments from various music videos."
Anyway, these mashups are happening all over the place using wikis, blogs, collaborative tools, and social networks. The biggest challenge in organizations is getting applications data base opened up using standard api's.
From an IBM spokesperson, "People want to be able to write programs to exploit new business opportunities, he said. - Companies have lots of databases they want to make mashable, he said, - and share with their business partners.