The comments on this post by Nik at TechCrunch are somewhat revealing about the actuality of mashup concepts.

Popfly might be used to create an interesting tool for synchronizing different kinds of communications and data into an educational weblog or library site.

At this point I can’t think of any mashup use except to modify something like Sphere to target kinds of journals and subject matter weblogs, but sphere may evolve to cover this anyway.