The Exam is fairly robust, and individuals cannot expect to do well with only a few hours of study. The Exam covers an extensive array of knowledge, fully described in the Exam Candidate Manual, and not all individuals will have come in contact with this during the course of their academic work or experience. However, the questions do come from those Knowledge Areas commonly encountered by active GISPs, and it is this minimal level of knowledge that a prospective GISP is expected to demonstrate in order to be approved for GISP Certification.
GISCI produced a practice exam, available in PDF form for download.
The first link is an updated and consolidated PDF version of the two Google Docs that follow. The two Google docs are open-edit materials regularly updated by the contributing geospatial community.
The GeoTech Center produces a free, online, personal-assessment survey as well as an online practice exam for further assessment of several Knowledge Areas on the Exam.
TeachMeGIS provides preparation classes for the Exam. Preparation classes take place in Houston and Oklahoma City, and online and evening online classes are available as well.
URISA offers workshops and webinars specifically for the Exam.