Foods with a high GI are metabolized into
glucose very quickly and tend to spike
blood sugars. These are difficult foods
for Type 2s to deal with. Often, these foods also taste very sweet and anecdotally, I've heard many folks (diabetic or not) report that if they have a little bit of candy/cake/cookies/sweet veges, then they crave more. All those foods are high GI foods.
GI is not the only factor to consider, of course.