Since the initial roll-out of "rich snippets" in 2009, Google made many improvements, here're recent updates:
- Testing tool improvements: Google added new error messages to rich snippets testing tool to help you better identify and fix any problems with the markup implementation. If you've added markup in past but haven't seen rich snippets appear for your site, try testing the markup again on updated testing tool.
- Added support for Breadcrumbs markup format that allows webmasters to explicitly identify the breadcrumb hierarchy on their pages. If breadcrumbs UI is already showing for your site, Google will show it even if you don't do markup.
- Events: If a web page containing events listings showed up in search results, up to three links to specific events could be shown in search result snippet. Google now show rich snippets when pages containing a single event show up in search results. Single event rich snippets now contain date and location of the event:
More Info: Documentation