Having just looked at many graduate school applications myself this article in the Boston Globe "Praising the low grade for a harder course" resonated with me. It notes how many college students shy away from the harder courses in order to maintain a high GPA in order to get into graduate school. Of course professors know this strategy and may actually prefer a student with a lower GPA who had taken more difficult courses to a student who has a high GPA with easy courses. Although there is no formal weighted GPA when applying to graduated school professors do it implicitly.