In case you missed it elsewhere, check out Mozilla Lab's video and blog post on Introducing Ubiquity - 'An experiment into connecting the Web with language'.
It's a framework that brings together lots of the bits of functionality that are available with browser extensions and bookmarklets and lets the user run them with natural language commands. One of the goals is to "enable on-demand, user-generated mashups with existing open Web APIs. (In other words, allowing everyone–not just Web developers–to remix the Web so it fits their needs, no matter what page they are on, or what they are doing.)".
It's a long way from being ubiquitous, but it does show that it's increasingly worth publishing your data in re-usable formats. They show an example of address being picked up from microformats in apartment listings and mapped for the user - that kind of mashup was possible before and they're a huge step forward in themselves, but how many users have the skills and time to do it? Being able to use natural language to pull together and use data could bring mash-ups to the general public in a massive way.