While I can’t guarantee whether it will or will not aid Google in showing breadcrumbs in search results, it seems to be working for my site. Just make sure you use the class “breadcrumbs” in the wrapping div (e.g. use the suggested basic usage code).
-John Havlik
Google does not immediately display breadcrumbs (takes up to a few weeks). You may find that using the Schema.org Breadcrumb microdata speeds up Google’s detection (but that is not always the case). See http://mtekk.us/archives/guides/using-schema-orgs-breadcrumb-microdata-with-breadcrumb-navxt/
If possible use WordPress SEO Plugin by Yoast. Their latest update now has the breadcrumbs with the rdf tags.
Google does not immediately display breadcrumbs but you can visit http://www.google.com/webmasters/tools/richsnippets to check if its displaying fine. If it works there, then its only a matter of time before Google starts displaying it.
The original Google breadcrumbs (RDFa and Microformat versions) have been deprecated. The Schema.org Breadcrumb microdata/format replaces the Google formats.