Yahoo's India team quietly launched Yahoo Glue out of the glare of the media circus around Yahoo these days. Glue has been noticed by a few commentators (e.g., TechCrunch), who mostly see it as response to Google's Universal Search (or Ask's search interface). They might be missing the point. Glue is fundamentally different from Universal Search and represents a whole new way of thinking about search.
The fundamental distinction is: where do the results come from? Google's Universal Search searches across Google's properties: web search, image search, YouTube, Scholar, Google News, and so on. Glue, on the other hand, includes not just Yahoo properties (web search, Yahoo! Answers, Flickr), but also pulls in results from WebMD, HowStuffWorks, and even (ironically) Google Blog Search and YouTube. For example, compare Universal Search (diabetes) with Glue (diabetes). In this respect, Glue bears more similarity to mashups such as Addict-o-Matic than to Universal Search.
The Web today is a far different place from what it was when Google's search paradigm was invented. The web was then a collection of documents; it is now a collection of applications. Applications such as Facebook, MySpace, YouTube, and Yelp. Each application has its own deep collection of data, and we tend to think of them as being different information types rather than just "web pages". Yet the search model flattens each of these rich interactive services into a collection of web pages that can be indexed -- that's really putting very new wine in a very old bottle.
The one-index-fits-all model forces a linear ranking of incomparable types, such as images, videos, how-to content, facts, and opinion. That's really comparing apples to oranges. The correct way is to deal with each of these information sources as a first class citizen, with its own kind of data and interaction paradigm. Let them compete for real estate on a 2-dimensional search results page (as opposed to 1-dimensional list), and may the best ones win.
Of course, there are many technical challenges to be solved in getting there. Sending each query to every web application is a recipe for disaster; and dealing with many different APIs is not conducive to scaling. To keep themselves relevant, however, search engines must evolve from indexes to intelligent routers of searches to third-party applications.