It is not recent the fact that people has reported seeing different features in the Google search user interface. It has been recognized that this might be just a test method used to debug new features, but no official word was said until today.
In the Google official blog, word has been made of the testing procedures used by the company:
... to learn more, we sometimes randomly select a group of people to see a possible improvement to search options. Or we may select a group of people and try out a new element while they're searching. If you ever wonder why your Google site looks slightly different from that of the person sitting next to you, this is why.Some of the features discussed in the article are already known, but this signs that Google is always trying to introduce new features, and using random people to test it. It is an interesting idea, that maybe other companies will try to emulate, if they ever want to compete with the pace of development at Google.
We are currently testing new ways to refine searches so that, for example, a search for jobs might offer a choice of job location or function, rather than forcing you to continually narrow the terms you type in to a standard Google search.