Does what you study in college matter? It certainly does when it comes to how much you'll make on average when you graduate. Counseling Psychology students just out of college make on average about $29K. Petroleum Engineers make about $100K above that figure.
http://cew.georgetown.edu/whatsitworth/
But what students study in college also matters a lot when it comes to how much students improve their critical thinking abilities. Interestingly, fields such as sociology and foreign languages appear to come out the best on this latter scale, with physical education and business close behind. Economics and Architecture bring up the rear. The author of the following piece has a few theories about why that might be.
http://www.insidehighered.com/views/2011/06/16/connor_essay_on_why_majors_matter_in_how_much_college_students_learn
Perhaps not surprisingly, these two sets of data are not at all correlated.