Information Architecture is the use of site diagrams and wireframes to organize web sites.

Card sorting is a way that many use as an input for the structure of a site or product. It is used because it is a quick, inexpensive & reliable method of organizing information.

The top mistakes are no structure, search & structure not integrated, missing category landing pages, extreme polyhierarchy, subsites poorly integrated with the main site, invisible navigation options, uncontrollable navigation elements,  inconsistent navigation, too many navigation techniques, & made up menu options.

What I take from it is that most people want to believe that the viewer will read all the information presented to them on a website about a product, service, or whatever, but in all reality all the viewer usually does is just scan over the pages picking up the main parts and leaving the small details unnoticed.