Here is an article I like a lot that shows just how bad a bad programmer can be. http://www.codinghorror.com/blog/archives/000781.html

Basically to sum it up, the author mentions a very simple question that he asks potential programming candidates to solve. This kind of question is the kind of question you can solve by making it through two/three chapters in any programming book, yet the number of people, even senior level developers, that can't get it is astonishing.