GIS is a fantastic tool. Hopefully you now have a better idea of how the tool works. It is a wonderful way to organize, analyze, and present spatial data. It won't fill all of our needs throughout the study of spatial epidemiology, but it will fill many; and by trying it out you will gain some important and valuable experience for the future.
Once you understand the issues discussed above, you should be ready to take on ArcView and the Illinois Cancer data that you'll encounter in this module's lab. While we've pointed out some of the pitfalls before you, we're certain that there are others lurking. Don't let them burst your bubble: grit your teeth, and scramble over those obstacles!