Bing released an enhanced page preview feature during November with a different interface and more focus on structured previews. For example a search for Carbon Credits is shown below, when you hover your mouse pointer over the search result an arrow pointing to the right in a gray box shows up, moving your mouse pointer over the arrow itself pops open a layer with a preview of text on the page.
In some situations, like the result from Wikipedia above, a site search box is also shown. We've observed many different variations in what the Bing preview will display. They all typically show some text content, but may also feature a list of popular and/or deep links on the site, site contact information, they may even show pictures if it's a Facebook page.
Some of this information can be useful to know, for example popular links show what Bing/MSN have tracked to be popular pages users view after landing on the page. We have to assume they are getting that data from the MSN toolbar – and this does give you some insight as to what's getting clicked on for yours, or a competitor's site.
Not every site owner will like this feature, If you don't want your content available by the Document Preview feature, you can opt-out using the meta robots tag. To specifically block only Bing from using a preview feature add the following tag to your pages head area.
<meta name="msnbot", content="nopreview">
Or, if you wish to block all engines that support the nopreview tag, use this generic version;
<meta name="robots" content="nopreview">
For more information on Google updates, please see our friends at SearchEngineNews.com.