This leads you also in a few additional directions, including: - Collective Intelligence (including crowdsourcing), - SOA, and - RIA in general.
RIA is especially worth considering because you're talking about marketing; it changes the interface to such an extent that the concept of a "page" is almost irrelevant. Making that concept even more irrelevant is hot - views, services and actions - until that back button disappears. And SOA, well... there are lots of directions there.
As far as less obvious case studies, try: - Amazon Web Services Group - lemonade.com - FaceBook Badges
And, of course, get some histories from Howard Rheingold's SMART MOBS and David Weinberger's SMALL PIECES LOOSELY JOINED. (Available on this thing call Paper. :)
Imho, something that brings two or more disparate systems together, rather than trying to reinvent the best features (with yet another login to maintain that identical data...), is going to be the next killer app.