The “When do we need them?” guidelines apply to location and attribute breadcrumbs, not so much to path breadcrumbs. (Path breadcrumbs are useless, for example, when you reach a lower-level page from outside the site.) The examples are beautiful, and would be even more helpful if they were grouped into the three types of breadcrumbs.

The identification and description of the three types of breadcrumbs come from Keith Instone’s work, which merits a citation in any discussion of this topic: http://instone.org/breadcrumbs/

See also Angela Colter’s work on how people use breadcrumbs: http://angelacolter.com/breadcrumbs/