Yesterday Google debuted Rich Snippets, a feature that enables webmasters to build on the "snippet" of content that appears for their sites in organic search results.

"Rich Snippets give users convenient summary information about their search results at a glance," writes Google's Webmaster Central Blog. "We are currently supporting data about reviews and people. When searching for a product or service, users can easily see reviews and ratings, and when searching for a person, they'll get help distinguishing between people with the same name."

Rich Snippets make it easier for webmasters to add more useful information to their listings in a format ideal for skimmers. The inclusion is based on research that suggests useful and relevant additions to organic search summaries increase the likelihood of click-through.

To display Rich Snippets, Google will trawl sites for markup formats (microformats and RDFa) that can, in most cases, simply be wrapped around existing webpage data with a few additional tags. The Webmaster Blog, linked above, provides examples of how the HTML should look with the microformats markup.

Because the service is rolling out gradually, webmasters that mark up their pages in preparation for Rich Snippets may not see immediate results. "[As] always we will use our own algorithms and policies to determine relevant snippets for users' queries," Google's Webmaster Blog team wrote. "We will use structured data when we are able to determine that it helps users find answers sooner."

However, standard annotations not only avail this structured data to Google search, but to any service or tool that supports the same standard. To prepare your site accordingly, read the documentation on marking up structured data.

Webmasters can also express their interest in Rich Snippets by filling out a form.

In the four weeks ending April 25th, Google accounted for 72.74% of all US searches, according to Hitwise. This represents a 7% increase from 67.93% last April, also up from 72.39% in March '09.