Google experiments with a lot of interesting new features, but not all of them are publicly available. A post from Google's blog inadvertently revealed some experiments, by showing a list of iterations for the "search options" feature released this week.
The initial concepts for the "search options" panel included a lot of interesting enhancements:
* grouping search results by topic
* grouping search results by people
* showing page previews for search results
* showing only pages that you've seen or pages you haven't seen before
Google has previously tested an interface that grouped search results in predefined categories like reference or reviews, but it's not clear if "group by topic" works in a similar way or it's a different approach. To search pages you've seen before, there's Google Web History, but it's very slow and the ranking algorithm needs a lot of improvement.