Remember how Borland used to advocate Query By Example (pronounced “cube”) to promote its Paradox database? Today, some web sites help users find a whole category from a single example. Instead of learning how download.com categorizes software, I can search for a specific program, then I’ll use the breadcrumb navigation to find others in the same category.
If your site supports navigation from detail to generic (see also how Amazon.com lists related categories for each product), then users will be able to cube it. It saves them random navigation through the site, or the effort to rationalize what they’re looking for. Such a system beats site maps hands down, because it relies on something users already know.