Website Usability Guidelines

Card Sorting Advantages

Simple Card sorts are easy for the organizer and the participants. Cheap and typically the cost is a stack of 3x5 index cards, sticky notes, a pen or printing labels, and your time.
Quick to execute and you can perform several sorts in a short period of time, which provides you with a significant amount of data. This established technique has been used for over 10 years by many designers.
Involves users because the information structure suggested by a card sort is based on real user input, not the gut feeling or strong opinions of a designer, information architect, or key stakeholder. It should be easier to use.
Card sorting provides a good foundation for the structure of a site or product.

Card Sorting Disadvantages

Does not consider users tasks. Card sorting is an inherently content-centric technique. If used without considering user's tasks. It may lead to an information structure that is not usable when users are attempting real tasks.
Results may vary. The card sort may provide fairly consistent results between participants, or may vary widely.
Analysis can be time consuming.
Participants may not consider what the content is about or how they would use it to complete a task. They may just sort it by surface characteristics such as document types.