I'm delighted to announce the release of the middleman-breadcrumbs gem, which provides a simple breadcrumbs generator for Middleman. Just install and activate the gem, and you'll be able to use
breadcrumbs(current_page) to generate something like
Home > Parent > Page based on the Middleman sitemap.
For more information, please visit http://www.github.com/marnen/middleman-breadcrumbs. Enjoy!