It seems that Google has started rolling out the structured data search update that it talked about a few months back, or at least is testing it on a large scale. Several types of searches, those with immediate answers, will not get an info box to the right of the search results, similar to the Google+ box, with information about the query as well as additional links.
The type of information varies with the query, but the box shows up for a large variety of searches, from questions like "what's the tallest building in the world," to actors and historical figures, to sports teams.
Wikipedia is almost always present in the info box, with a link pointing to the query's, be it an actor, a landmark, or a band, Wikipedia page.
But the info box provides more than just a snippet of text from Wikipedia and a link, that's what regular search results do, it also lists all sorts of data about the query, date and place of birth for famous people, height and date of construction for buildings, singles and albums for bands and so on.
What's interesting is that Google doesn't seem to be pointing to its other services all that much with the info box. The links are to the Wikipedia pages or to new Google searches, with the exception of Google Maps links.
Google has been working on utilizing structured data to more effect for a long while now. Google Squared was a search engine designed specifically for structured data. But it's a tough problem, the web is a very unstructured place, there's plenty of information, but it's hard to put in context and merge different sources.
Search engines have been encouraging websites to use more and more metadata to describe various types of content and data, but that's not enough, Google has also been working on improving the algorithms that make sense of the data on the web.
The feature is in testing, or is being rolled out for now, there's a chance of seeing it in action on google.co.uk, you can try signing in or singing out of your account to see if it works.