Our SEO consultants recommended them -- whether or not you expose them to the user, they can help keyword crawl. More here: http://usabilitygeek.com/12-effective-guidelines-for-breadcrumb-usability-and-seo/,
(I posted this article mainly for it's SEO benefits).
Current eCommerce sites: Gilt, Target, Amazon & Zappos (though inconsistent). I prefer Gilt's subtle implementation.