Google tested many interfaces for displaying related searches: at the bottom of the page, above the search results, in the left or right sidebar. A recent experiment adds some related searches to the toolbelt, the sidebar that includes many advanced options.
Alistair Lattimore noticed that a search for [Circle on Cavill] returned a big list of refinements in the sidebar: restaurants, retail, apartments, for sale, map, parking, hotel, movies. Selecting one of the suggestions changed the query to [Circle on Cavill restaurants] or [Circle on Cavill retail], even though the search box didn't change the query.
Some would say that Google borrowed a Bing feature, even if Google tested it earlier or Hakia used it before Bing. What I find troubling is that Google combines site categorization filters like forums or reviews with search refinements.