Will valid markup now help your Google ranking?
Google recently published a list of 30 updates made to search over the tail end of 2011. Tucked away in the middle of the list is mention of improved support for rich snippets. The snippet types listed are shopping, recipes and reviews. Amongst the other information on rich snippets is listed a point that a snippet can only be given for a page with a single item upon it, ruling out snippets for things like searches for ipods on amazon.
However it looks like google has also been testing out ways of extracting structured data from pages which have no defined snippet and contain multiple items - starting with real estate classifieds. What's equally interesting here is that it seems having clear and valid markup may have an extra impact on your site's appearance in the Google results and number of visitors clicking through!