"Classification (taxonomy, categorization) is to content as mapping is to geography. It is an essential tool that allows the person visiting a Web site to navigate it quickly and efficiently. Without professional classification, a Web site becomes a jumble of content that is confusing and time wasting."
Classification starts even before you put content on the web. Think about product and product range names that would make sense. Now look at notebook and printer vendors for worst practices. Do you want the Xyz2000, the YHZ800L, or the Z8L-XXL? And these guys wonder why people stop buying their stuff.