During my Junior year of college, Facebook was still in the process of rolling out from school to school. Initially I fought the urge to join but with the help of some liquid courage and the prodding of my roommate, I finally bit the bullet and never looked back.
My initial fear was less about the effect Facebook would have on my grades and more an aversion to having my friends make a permanent record of my life in college. In retrospect, these fears were reasonable.
Even if my fears were grounded in protecting my GPA, a recent study in Computers in Human Behavior demonstrates that Facebook has no statistically important consequence upon the grades of students who use the service frequently. In fact, their study showed that users who rely on Facebook for largely informational practices (commonly known as Facebook stalking) demonstrate higher GPAs.
Although this is an isolated study the subject requires greater investigation, I find it interesting that more and more sources are saying that minor distractions like social networking can have a positive impact upon productivity.