Google have released “Rich Snippets for Google web search,” a new presentation of snippets that highlight structured data embedded in web pages. Rich Snippets provide summary information, including important page-specific attributes, to help you quickly identify the relevance of your results. Since Custom Search sits on top of the Google web search platform, Rich Snippets are enabled for custom search engines too. if you're using Custom Search or Site Search on your website, you can now control further how your content appears in search results. You can showcase key information -- such as image thumbnails, summaries, ratings, and prices -- in your result snippets if you provide the appropriate markup on your pages. At this time, Rich Snippets attribute information for Custom Search is only returned in XML (via <PageMap> tags), so you can use your own customized presentation controls.
More info: Google CSE Blog