My mind is reeling as I look over what Google is offering through the Subscribed Links API. Basically, this is a topic-driven widget that appears at the top of search results. To build one and offer it to the world, it says I need to define a set of xml files for the query patterns, output format, preferred url annotations, and "labels" allowing the results to be further winnowed down.

With the Google Subscribed Links API, you can add your services directly into Google search. This can help make those services more accessible, giving your users another entry-point to them when they're making a related search on Google. Source: Subscribed Links API.

The Topics Developer's Guide delves into the url annotation and the "labels" winnowing:

A label is a mechanism for modifying the Google ranking function. The modifications can range from a hard restrict to a specified set of documents to a subtle twiddling of results. The modifications come in effect when you enter a query and then click on a label. Source: Topics Developer's Guide.

Mmore can be found in the FAQ.

Continuing the "Googlemantic Web" theme from my previous comments, one thing I'd like to know more about is the "Data Object" types. I can define my own, but Google defines special types such as cities, regular expression matches, and dates.