Jakob Nielsen on breadcrumbs

Breadcrumbs is good for online navigation. Implement it and you'll delight the users...

• Breadcrumbs show people their current location relative to higher-level concepts, helping them understand where they are in relation to the rest of the site.
• Breadcrumbs afford one-click access to higher site levels and thus rescue users who parachute into very specific but inappropriate destinations through search or deep links.
• Breadcrumbs never cause problems in user testing: people might overlook this small design element, but they never misinterpret breadcrumb trails or have trouble operating them.
• Breadcrumbs take up very little space on the page. (via AlertBox)