first things first, Breadcrumbs are called that way because they are a good analogy to the trail of crumbs that Hansel dropped in the woods so that he and Gretel could find their way back home. So in the primitive form that breadcrumbs where introduced they were meant to show you the path from where you are and back to the homepage. A few years back, information behemoths like Yahoo uses effectively breadcrumbs to navigate it's enormous database listing that was built on very deep hierarchies.
To the common beliefs, breadcrumbs on their own are not a good substitute of a complete navigation scheme. They are very effective in providing navigation down a specific cognitive tree/hierarchy of similar information but not convenient for full wandering around the website. Some research has shown that users mostly use them to go back one level or find their way back to home.
Finally, some studies have shown that if you're to use them, put them at the top in a prominent place but never use them instead of a page name. Also make sure you use ">" between levels since it's the most known pattern, always highlight the last item, which is supposed to be the current page and use visual clues like "You are here" before them.
Hope that helps you go the right direction.