I discovered this new feature as I was doing my usual searching on Google. If you do a Google search, apart from the ability to do Instant Search, clicking on a search result (not the result title, but the result description) or the magnifying glass will not just return a screenshot of the page in question, if the search terms are part of the website’s content, it will also highlight where the keyword is found! Certainly a very cool feature.
Not all results give a preview yet, since this service is probably very new, but I discovered that if you ask for a preview from a result more than once, it will “force” Google to go do a screenshot for that website.
Go try it out!