In the end I decided to stick with a more traditional grading system for this semester. I couldn't come up with a reason for using badges besides "they're hot right now." Since this is a class for first-year students it made more sense to familiarize them with the typical college grading system. Maybe in the spring I'll get more exciting.
However, this class--Current Topics in American Ed--will be blogging throughout the semester. You can read the posts at CurrentTopicsAFC.org.