There has been quite a bit of buzz about Rod Smith's keynote at last week's NYPHP Conference & Expo. Rod and his team provided a case study of a situational application built for the National Association of Broadcasters and performed a live demo of how to go about creating a five minute application.
It was pretty interesting stuff, but Rasmus Lerdorf followed with what I found to be an even more impressive mashup that the audience could better relate to. He showed a tool he built for internal use at Yahoo which serves as an corporate Craig's List of sorts, with hooks to Web services to provide posters with recommended price ranges and stock photos of the item they are selling.
He mentions that the real technology that made these two applications as "cool" as they are and really makes them possible is Ajax - both use it to pull the data from the Web services in.