If Microsoft was able to re-launched their search engine as Bing nowadays which is most likely to be user-interface related in most of its changes, Google announced its ‘secret project’ Caffeine which includes infrastructure-related changes but no user-interface. In a way, Caffeine affected Google’s user-interface as its infrastructure is new.
This Caffeine is considered to be the ‘next-generation architecture for Google’s web search.’ It includes changes in crawling, indexing and ranking pages though Google says that the new architecture is primarily changed based in how they index.
Google said that they are not trying to integrate this new architecture on the current one; this is a developer preview where webmasters and power searchers can experiment and provide some feedbacks. But compared to the defunct Google’s SearchMash which was also intended for experiments, Caffeine will soon replace the existing Google architecture.