Here's an explanation of Research Trails taken from the paper's abstract:
We propose the concept of research trails to help web users create and reestablish context across fragmented research processes without requiring them to explicitly structure and organize the material. A research trail is an ordered sequence of web pages that were accessed as part of a larger investigation; they are automatically constructed by filtering and organizing users’ activity history, using a combination of semantic and activity based criteria for grouping similar visited web pages. The design was informed by an ethnographic study of ordinary people doing research on the web, emphasizing a need to support research processes that are fragmented and where the research question is still in formation. This paper motivates and describes our algorithms for generating research trails.Sounds like this will be a great addition to Google's suite of tools.