The plugin uses a CSS hack to show the date – your visitors see it, but Google takes it for the “title” parameter of a “span” element and does not consider it to be a part of the page content. Therefore, the publishing date is not shown in the search snippet.
The plugin works with ALL themes now (from version 2.00).
If you liked my plugin, please rate it.
This plugin is available for download to be used on your WordPress self-hosted installation.