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.