Google has recently started including snap shoots of pages in their search results. Although not all users may be using them. It also can not yet be seen as a feature that will not change.
They appear when the magnifying class is clicked or when the text is clicked on the search engine listing. Once preview is on hovering over the listing shows an image of the site. And when on page content exists for the search terms those are magnified on the preview.
Increasing click through rates to the sites using the preview boils down to above the fold design. Flash and canvas show as blank space … jquery shows as the initial display before and script is ran and there are a few rendering differences from html5.
Speculation is that people may dig farther down the search results page in their selection process.
Bounce rates may also be effected.